Changed CForStmt. Updated parser for ident, var, lets, and switch

[MichaelS11]

This has the changes from #268 in it.
Did some rework of switch, so that PR would conflict.

[codecov-io]

Codecov Report

Merging #271 into master will decrease coverage by 0.34%.
The diff coverage is 95.83%.

@@            Coverage Diff             @@
##           master     #271      +/-   ##
==========================================
- Coverage   82.22%   81.87%   -0.35%     
==========================================
  Files           8        8              
  Lines        1879     1876       -3     
==========================================
- Hits         1545     1536       -9     
- Misses        246      256      +10     
+ Partials       88       84       -4

Impacted Files	Coverage Δ
vm/vm.go	83.69% <0%> (ø)	⬆️
vm/vmExprFunction.go	69.63% <100%> (ø)	⬆️
vm/vmExpr.go	81.89% <100%> (-1.82%)	⬇️
vm/vmStmt.go	82.9% <100%> (+1.23%)	⬆️
vm/vmConvertToX.go	55.38% <80%> (ø)	⬆️

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[MichaelS11]

This is a first pass on fixing some of the parsing of var/let in the for loop. Got side tracked into the switch code.

Thought it would be good to merge before too much code change.

[MichaelS11]

Fix when map item is not found it is not equal to nil and should be.
#272

[mattn]

Thank you