Support for Alternative Input Sources

[j-mie6]

Parsley currently accepts providing input as a String and parsing directly from a File. However, the file support is limited, and still reads in the entire file into memory in advance. It would be nicer to support a more generic system for providing input, including from InputStream. Preliminary work has been performed towards this in https://github.com/minut1bc/Parsley/tree/stream, but incorporating this may take some time and further optimisation and porting to Parsley 4 is required.