Implement the main loop

[bahmanm]

Build a main loop and fix the potential plumbing problems in how the system works for the loop to work.

[bahmanm]

The line in Primitive which used to set NIP has been removed.

It's a rather drastic departure from the initial implementation.

The reason behind this is to mimic free assmebler jmps in JONESFORTH which was previously impossible as next would overwrite NIP after every execution.

[bahmanm]

All tests that verify the value of NIP must be modified to adapt to the new Primitive#call().

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.64%. Comparing base (f2caefd) to head (cff1d4d).

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #180      +/-   ##
============================================
- Coverage     82.89%   81.64%   -1.26%     
- Complexity      384      385       +1     
============================================
  Files            87       87              
  Lines          1479     1509      +30     
  Branches        214      216       +2     
============================================
+ Hits           1226     1232       +6     
- Misses          186      207      +21     
- Partials         67       70       +3     

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