Splits corpus building off from autocomplete

* Creates new module, prefixcorpus, that can be used for all corpus creation utilities
* changes the __main__ fn of autocomplete to be autocomplete without terminal altering
Temporarily disables keypress utility (bugfix needed - see commit log)

*removes other unnecessary imports
Alters find function to return immediately if a valid term is
not passed as a parameter
Makes tokenfn parameter of the Corpus constructor

*defaults to token()
*deprecates tokenize fn because unused (duplicates the work of Corpus.text+
 words+self.words)
Renames corpus/ --> sampletexts/

*moves complete works of shakespeare (in one file into above folder)
*renames file from shakespeare.txt -> sampletexts/allshakespeare.txt
*alters to autocomplete.py to be consistent with changes
Changes get_files function to correct location of current default folders
Moves get_files & make_files functions to the prefixcorpus module

*Example Usage:
   (1) files = get_files() # get an iterator for the filenames in nested folders
   (2) make_file(files,'corpus.txt') # make a single file in the same directory called corpus.txt
   (3) new_corpus = Corpus('corpus.txt') # returns a prefix-tree corpus containing all tokens in the
   files from (1)
First sketch of autocomplete README

Adds the following sections:
* contents
* examples (1 at present)
* requirements
* benchmarks

To-DO:
* add examples to README.md
* add tests to files & document in the README.md
* add notes
* add To-Do list
Adds To-Do list to README