Make `pip show` show much more metadata

New fields:
  - Metadata-Version
  - Summary
  - Home-Page
  - Author
  - Author-email
  - License
  - Entry-points

Sample output:

    $ pip show pytest
    ---
    Metadata-Version: 1.1
    Name: pytest
    Version: 2.6.4
    Summary: pytest: simple powerful testing with Python
    Home-page: http://pytest.org
    Author: Holger Krekel, Benjamin Peterson, Ronny Pfannschmidt, Floris Bruynooghe and others
    Author-email: holger at merlinux.eu
    License: MIT license
    Location: /Users/marca/python/virtualenvs/tmp-4e2169280f5cbd16/lib/python3.4/site-packages
    Requires: py
    Entry points:
      [console_scripts]
      py.test = pytest:main
      py.test-3.4 = pytest:main
Do some gymnastic to respect a certificate configured via config file
Merge branch 'master' into develop
Correct the spelling
Merge branch 'master' into develop
Update installing.rst

Resolve merge conflict on updating on Windows.
Merge pull request #2262 from msabramo/patch-3

Update installing.rst
Fix pep8 issue
Switch to 6.1.0 for our next release instead.
Add PEP 440 to the change log
Don't return cached output for InstallRequirement().installed_version
Merge pull request #2264 from dstufft/add-pep440-changelog

Add PEP 440 to the change log
Merge pull request #2263 from dstufft/correct-version-output

Don't return cached output for InstallRequirement().installed_version
Fix pep8 issue
Bump version for development of 6.0.2
Update installing.rst

Resolve merge conflict on updating on Windows.
Add PEP 440 to the change log
Don't return cached output for InstallRequirement().installed_version
Bump for release of 6.0.2
Merge branch 'release/6.0.2'