Add '--no-logs' option to argument parser

[adamjsawicki]

Fixes #8.

Also throws custom Exception if nltk or its needed modules are not properly installed.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@f3292d5). Click here to learn what that means.
The diff coverage is 98.41%.

@@            Coverage Diff            @@
##             master      #22   +/-   ##
=========================================
  Coverage          ?   94.97%           
=========================================
  Files             ?       10           
  Lines             ?      338           
  Branches          ?        0           
=========================================
  Hits              ?      321           
  Misses            ?       17           
  Partials          ?        0

Impacted Files	Coverage Δ
rnlp/tests/rnlptests/test_parse.py	100% <100%> (ø)
rnlp/tests/rnlptests/test_converter.py	100% <100%> (ø)
rnlp/tests/rnlptests/test_textprocessing.py	100% <100%> (ø)
rnlp/tests/tests.py	90.9% <66.66%> (ø)
rnlp/parse.py	98.23% <98.33%> (ø)

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[hayesall]

LGTM! The Travis build threw an error, but with 2.7 being end-of-life I'm not worried.

I'll make a maintenance update to drop it.