adds Dockerfile
fixes path so Docker runs for everybody...
adds pstotext to Dockerfile
first crack at setting up class-based parsers
updated CONTRIBUTING guide for class-based parsers
converted the rest of the parsers to subclassing textract.parsers.utils.BaseParser
fixed pptx parser
unicode sandwich! (for anything that uses a ShellParser)
unicode sandwich for all!
not using the md5 function
Merge branch 'master' into docker
standardized documentation on the Parser classes
updated documentation with a few things in anticipation of merging in the class-based parsers
Shuffling things around for Docker

* Consolidates requirements, provision, and docker directories.
updates Travis file for dir change
Updates to requirements scripts.

An attempt to make it work both with Travis and Docker.
Remove Docker container after run.

Otherwise it piles up multiple containers you probably don't need.
got everything merged in from master, including xls/xlsx parsers and all bug fixes
ignoring incompatible code points when re-encoding to byte-strings
Merge branch 'master' into docker