update diagrams for buildspec structure and Parser.

[shahzebsiddiqui]

Update documentation.

[codecov]

Codecov Report

Merging #678 (a95fe28) into devel (dbddad0) will increase coverage by 11.05%.
The diff coverage is 65.75%.

@@             Coverage Diff             @@
##            devel     #678       +/-   ##
===========================================
+ Coverage   57.69%   68.75%   +11.05%     
===========================================
  Files          21       34       +13     
  Lines        1553     2883     +1330     
  Branches      226      537      +311     
===========================================
+ Hits          896     1982     +1086     
- Misses        606      762      +156     
- Partials       51      139       +88     

Impacted Files	Coverage Δ
buildtest/log.py	63.16% <ø> (ø)
buildtest/executors/slurm.py	14.17% <14.17%> (ø)
buildtest/executors/cobalt.py	16.07% <16.07%> (ø)
buildtest/executors/lsf.py	17.48% <17.48%> (ø)
buildtest/menu/__init__.py	44.44% <34.78%> (+23.75%)	⬆️
buildtest/menu/compilers.py	41.12% <41.12%> (ø)
buildtest/executors/setup.py	42.39% <42.39%> (ø)
buildtest/config.py	44.80% <42.98%> (-55.20%)	⬇️
buildtest/docs.py	60.00% <60.00%> (ø)
buildtest/menu/build.py	62.21% <61.32%> (+36.59%)	⬆️
... and 41 more

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