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An easy way to get started that doesn't use pure ML is Markovify [1]. I used it for a couple of projects last year.

This blog post and associated github give a good enough intro to get simple examples working: http://karpathy.github.io/2015/05/21/rnn-effectiveness/

I may open source it. It's pretty easy to get started if you leverage pre-existing libraries for Markov chains and Twitter ingestion.