This is a simplified Python pandemic simulator based on infection properties of COVID-19. The inspiration was to
test different quarantine models on the total number of infected (for example, only quarantining the elderly and at-risk to
achieve faster herd immunity and reduce total deaths). However, this simulator is still far too simple to draw meaningful 
conclusions.

Contributions are welcome, especially ones that make the model more realistic without being too computationally expensive, or
which provide a means to create a digital graphic of the spread of the disease over time.

Requirements:
pandas

Recommended:
pypy (for speed)

Example:
%run "virus_sim.py"
w = World(20000, 10, 1)  # 20,000 people in the "World", randomly distributed on the default 200x200 world-grid, with 10 initially infected who are able to expose people up to 1 tile away in each direction. People move around daily according to their age.
df = w.run_simulation(100)  # Run simulation for 100 days.
df
Out[005]: 
   Population Infected Recovered Dead
0       20000       13         0    0
1       20000       18         0    0
2       20000       23         0    0
3       20000       28         0    0
4       20000       32         0    0
5       20000       42         0    0
6       20000       46         0    0
7       20000       55         0    0
8       20000       63         0    0
9       20000       73         7    0
10      20000       87        10    0
11      20000       95        15    0
12      20000      108        17    0
13      20000      113        24    0
14      20000      135        28    0
15      20000      152        39    0
16      20000      176        43    0
17      20000      197        49    0
18      20000      216        58    0
19      20000      239        73    0
20      20000      278        86    0
21      20000      302       100    0
22      20000      342       117    0
23      20000      379       129    0
24      19999      426       145    1
25      19999      481       172    1
26      19998      549       196    2
27      19997      619       220    3
28      19996      680       252    4
29      19995      765       286    5
30      19995      852       330    5
31      19995      957       382    5
32      19995     1083       422    5
33      19995     1220       470    5
34      19993     1350       528    7
35      19993     1471       607    7
36      19993     1597       683    7
37      19992     1745       771    8
38      19988     1873       864   12
39      19986     2028       968   14
40      19985     2145      1092   15
41      19980     2265      1222   20
42      19977     2367      1381   23
43      19973     2512      1534   27
44      19971     2654      1704   29
45      19966     2733      1910   34
46      19961     2828      2114   39
47      19959     2938      2308   41
48      19955     3040      2517   45
49      19947     3083      2763   53
50      19941     3174      3001   59
51      19935     3223      3268   65
52      19928     3298      3528   72
53      19919     3330      3787   81
54      19911     3368      4064   89
55      19910     3410      4347   90
56      19900     3422      4616  100
57      19896     3399      4927  104
58      19888     3385      5234  112
59      19880     3369      5529  120
60      19874     3341      5834  126
61      19868     3292      6134  132
62      19861     3253      6433  139
63      19857     3140      6769  143
64      19848     3027      7091  152
65      19845     2942      7386  155
66      19842     2849      7696  158
67      19838     2768      7975  162
68      19833     2629      8299  167
69      19826     2558      8556  174
70      19823     2404      8850  177
71      19814     2271      9121  186
72      19809     2159      9382  191
73      19806     2059      9622  194
74      19802     1955      9846  198
75      19797     1849     10064  203
76      19794     1763     10267  206
77      19790     1653     10485  210
78      19787     1562     10675  213
79      19784     1465     10867  216
80      19781     1382     11023  219
81      19779     1278     11204  221
82      19772     1183     11362  228
83      19767     1118     11492  233
84      19765     1044     11617  235
85      19760      972     11731  240
86      19758      892     11873  242
87      19756      803     11994  244
88      19756      730     12106  244
89      19756      687     12191  244
90      19753      602     12299  247
91      19748      557     12367  252
92      19747      493     12451  253
93      19746      457     12509  254
94      19746      405     12580  254
95      19743      368     12633  257
96      19743      333     12690  257
97      19741      308     12728  259
98      19738      280     12765  262
99      19738      257     12797  262