Rename Fortran classes used for AST

[gnikit]

Fixes #109

[codecov]

Codecov Report

Merging #111 (cb49437) into master (c986bb4) will increase coverage by 0.36%.
The diff coverage is 94.28%.

@@            Coverage Diff             @@
##           master     #111      +/-   ##
==========================================
+ Coverage   84.97%   85.34%   +0.36%     
==========================================
  Files          11       11              
  Lines        4374     4374              
==========================================
+ Hits         3717     3733      +16     
+ Misses        657      641      -16     

Impacted Files	Coverage Δ
fortls/objects.py	82.95% <90.16%> (+1.13%)	⬆️
fortls/parse_fortran.py	87.73% <95.74%> (ø)
fortls/ftypes.py	100.00% <100.00%> (ø)
fortls/intrinsics.py	95.55% <100.00%> (ø)
fortls/langserver.py	82.39% <100.00%> (ø)

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