Use dummy renderer when checking inside is_paragraph.

[NEricN]

While the internal renderer is idempotent, an external application could have rendering functions that aren't. (e.g. keep track of how many times a function is called) This replaces the original renderer with a dummy renderer with no rendering functions in is_paragraph, so that no actual rendering is done.

[codecov-io]

Current coverage is 62.09% (diff: 100%)

Merging #32 into master will increase coverage by 0.16%

@@             master        #32   diff @@
==========================================
  Files            14         14          
  Lines          3854       3860     +6   
  Methods         255        255          
  Messages          0          0          
  Branches       1037       1037          
==========================================
+ Hits           2387       2397    +10   
  Misses         1030       1030          
+ Partials        437        433     -4   

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[kjdev]

Thanks.