OCCA enum and union support

[kian-ohara]

Added support for (typedef) enums and (typedef) unions.

[mkbosmans]

We have tested this on our side and it correctly handles enums and unions now in kernel code.

[codecov]

Codecov Report

Merging #705 (76d62de) into development (adde964) will decrease coverage by 0.99%.
The diff coverage is 45.86%.

❗ Current head 76d62de differs from pull request most recent head 84f843e. Consider uploading reports for the commit 84f843e to get more accurate results

Additional details and impacted files

@@               Coverage Diff               @@
##           development     #705      +/-   ##
===============================================
- Coverage        76.24%   75.25%   -0.99%     
===============================================
  Files              292      297       +5     
  Lines            18826    19324     +498     
===============================================
+ Hits             14354    14543     +189     
- Misses            4472     4781     +309     

Files Changed	Coverage Δ
include/occa/dtype/dtype.hpp	0.00% <0.00%> (ø)
src/occa/internal/lang/type/typedef.cpp	70.37% <ø> (-1.06%)	⬇️
src/occa/internal/lang/type/vartype.cpp	84.52% <28.57%> (-3.30%)	⬇️
src/occa/internal/lang/type/union.cpp	33.96% <29.78%> (+33.96%)	⬆️
src/dtype/dtype.cpp	51.67% <35.11%> (-23.67%)	⬇️
src/occa/internal/lang/enumerator.cpp	36.00% <36.00%> (ø)
src/occa/internal/lang/type/enum.cpp	40.00% <36.73%> (+40.00%)	⬆️
src/occa/internal/lang/loaders/typeLoader.cpp	79.00% <63.51%> (-6.08%)	⬇️
src/occa/internal/lang/loaders/unionLoader.cpp	64.70% <64.70%> (ø)
src/occa/internal/lang/loaders/enumLoader.cpp	83.72% <83.72%> (ø)
... and 3 more

... and 3 files with indirect coverage changes

[mkbosmans]

Would this be still in time to go in the 1.6 release?