DOC: Add explicit listing of dependencies in separate file.
FIX: Correct DEPENDS.txt formatting to pip guidelines

Despite these being checked upon running setup.py, these changes allow
`pip install -r DEPENDS.txt` to work properly.
FIX: Use `-e .` for Pip to install using requirements in setup.py
Merge pull request #13 from JDWarner/add_depends

DOC: Add explicit listing of dependencies in separate file.