extensible abbreviations

[D-Se]

Add support for more type checks, and implement scaffolding to extend the package for custom types.

To add new types:

• Create and entry in the abb.h file
• Add an entry to the is function in ifelse.c

[codecov]

Codecov Report

Attention: 22 lines in your changes are missing coverage. Please review.

Comparison is base (a86dd18) 90.64% compared to head (09e2c80) 81.73%.

Files	Patch %	Lines
src/isas.c	56.86%	22 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #19      +/-   ##
==========================================
- Coverage   90.64%   81.73%   -8.92%     
==========================================
  Files           5        5              
  Lines         171      208      +37     
==========================================
+ Hits          155      170      +15     
- Misses         16       38      +22     

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