Solved the w/o problem and added sdcard.fth

[Jos-Ven]

Also moved path to one location and changed files.fth so it can also be used for SDcards.

[Jos-Ven]

Improved f>d and the usage of an SDcard.

[Jos-Ven]

Changes in #137:

• Solves the problem with w/o files.
• Makes it possible to use an sdcard.
• The new words in files.fth makes it possible to switch
  between spiffs and the sdcard.
• The new layout of ls/dir also shows the total used bytes.
• The added setvbuf can be important when you encounter
  performance problems with the use of an sdcard.
• fetching.fth makes it possible to make a SVG-plot from data
  that on an sdcard without having to load whole data records.
• Increasing the accuracy of f>d. E.G. Old version:
  f# 1728733625848.770e0 f>d f# 1728733616479.531e0 f>d d- d. 0 \ Returned 0
  New version:
  f# 1728733625848.770e0 f>d f# 1728733616479.531e0 f>d d- d. 9369 \ which is right when rounded.

That also concludes this round of updates.