add some helpful predicates

[lime-green]

These predicates are meant to be general-use (call node) predicates to be used for visitor and inference-tip functions

[codecov[bot]]

Codecov Report

Merging #60 into master will increase coverage by 0.42%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #60      +/-   ##
==========================================
+ Coverage   93.41%   93.83%   +0.42%     
==========================================
  Files          10       11       +1     
  Lines         395      422      +27     
  Branches       57       64       +7     
==========================================
+ Hits          369      396      +27     
  Misses         15       15              
  Partials       11       11

Flag	Coverage Δ
#py27	93.83% <100%> (+0.42%)	:arrow_up:
#py36	93.83% <100%> (+0.42%)	:arrow_up:
#py37	93.83% <100%> (+0.42%)	:arrow_up:

Impacted Files	Coverage Δ
codewatch/__init__.py	100% <100%> (ø)	:arrow_up:
codewatch/predicates.py	100% <100%> (ø)

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