Improve documentation with a "common tasks" section

[vlandham]

This could be a separate page, or integrated in some way with the quickstart guide.

@arnicas has provided a great starting point for common tasks below. This could be used for inspiration:

Some recipes:

Tokenizing

• Split into words and punct, and remove punctuation:textkit text2words test_data/alice.txt | textkit filterpunc | more
• Split and lowercase: textkit text2words test_data/alice.txt | textkit lowercase - | more

  Stopwords

• Split into words and punc, remove punct, remove default stopwords: textkit text2words test_data/alice.txt | textkit filterpunc | textkit filterwords
• Tokenize, remove punc, remove default stops and a custom list: textkit text2words test_data/alice.txt | textkit filterpunc | textkit filterwords --custom custom/stop.txt | more
• Same, plus lowercase it all: textkit text2words test_data/alice.txt | textkit filterpunc | textkit filterwords --custom custom/stop.txt | textkit lowercase - | more

  Word counting

• textkit text2words test_data/alice.txt | textkit filterpunc | textkit filterwords --custom custom/stop.txt | textkit tokens2counts | more

  Bigrams

[I'm a little weirded out not getting counts out of these topbigrams results, or some other measure.]

• textkit text2words test_data/alice.txt | textkit lowercase - | textkit filterpunc | textkit filterwords --custom custom/stop.txt | textkit topbigrams | more
• Get bigrams without stopwords, lowercase: textkit text2words test_data/alice.txt | textkit filterpunc | textkit lowercase - | textkit filterwords --custom custom/stop.txt | textkit words2bigrams | more
• Count bigrams after filtering for stopwords: textkit text2words test_data/alice.txt | textkit filterpunc | textkit lowercase - | textkit filterwords --custom custom/stop.txt | textkit words2bigrams | textkit tokens2counts | more

  POS

• Get parts-of-speech for the doc (tokenize, then POS): textkit text2words test_data/alice.txt | textkit tokens2pos
• Get just the NNPs: textkit text2words test_data/alice.txt | textkit tokens2pos - | grep NNP
• Count the NNPs: textkit text2words test_data/alice.txt | textkit tokens2pos - | grep NNP | textkit tokens2counts | more