Added tagid output and argument subparsers

Switching between swid output and tagid output
happens via subcommands swid and tagid (tnc-ba/strongTNC#63)
Moved software ID generator to separate file
Renamed `tagid` to `software-id`
Updated help strings and README.rst
Moved generators to separate package
Added targeted request option & test

- Updated README
- Added --match option to argumentparser
- Added help for targeted requests
Included architecture in Software ID
Added setup.py to make the SWID generator easily installable

The swid_generator script can now be installed to your local PYTHONPATH
with ::

    python setup.py install

To install only symlinks to the sourcefiles (which means that code
changes are immediately reflected in the installation), use ::

    pip install -e .

Refs tnc-ba/strongTNC#40.
Changed to use rpm instead of yum

Fixes tnc-ba/strongTNC/issues/108

Removed debug print

Removed dependency section from Readme

Renamed environment from yum to rpm
Updated README changed yum to rpm
Changed --environment option to be rpm
Introduced visitor for output generation

Added visitor to print output, no caching in list anymore

Moved document_separator to visitor

Cleaned up comments

Removed debug print

Style fixes + print function

- Imported print function
- Removed unnecessary parens from from if
- Removed unused import

Added file encoding header
Changed identation of pretty output from tab to two spaces

Fixes https://github.com/tnc-ba/swidGenerator/issues/14
Removed extra newline from `software-id` mode

Fixes https://github.com/tnc-ba/swidGenerator/issues/15
Removed visitor pattern and introduced generators

- Introducing generators allows lazy generation of software-ids and SWID
tags
- Removed print visitor. Output printing is now done with a print function which takes the generator

Added docstring to create_swid_tags method

Changed to use relative imports

Removed obvious keyword from create_swid_tags and create_software_ids

Moved closing parenthesis to previous line

Removed unneeded parentheses

Changed docstring for create_swid_tags

Removed unused parameter
Switched license to MIT

- Updated information in setup.py
- Added LICENSE.txt
- Added license information to `swid_generator/main.py` and `README.rst`

Fixes tnc-ba/strongTNC#97.
Added .coveragerc
Fixed name of program in usage output
Abstracted away generator printing

Refs tnc-ba/strongTNC#110.
Renamed swidgenerator_argumentparser module

The module `swidgenerator_argumentparser` is now simply called
`argparser`. The context is obvious at import time due to the relative
import.