Make deepvirfinder pip installable

[papanikos]

Hello,

I wanted to make this available through conda eventually, started off with pip.

Current changes include

• Restructure directories to conform to PyPA format.
• Only code changes to the dvf.py script have been made. These include:
  • Automatic detection of the models dir, hoping it is useful when pip installed.
  • Dropped the optparse module in favor of argparse.
  • Minor refactoring to something more readable
  • Reporting on number of sequences and not lines (still with print statements)
  • The interface to dvf.py has changed to $ dvf.py -h (instead of $ python dvf.py -h)

If you agree with this, we should bump the version to 1.0.0 before merging- for now I used 0.9-beta for testing.

I tested this with python 3.6 and 3.7, seems ok.

For anyone interested, this worked for me on Ubuntu

$ conda create -n dvf_test python=3.6 # or 3.7
$ conda activate dvf_test
(dvf_test)$ pip install https://github.com/papanikos/DeepVirFinder/archive/v0.9-beta.tar.gz
(dvf_test)$ dvf.py -h