Add note about updating system path

Remind users to update system path since script does not. 

Well, at least on Windows it doesn't update PATH. Perhaps this should be qualified?
Merge pull request #1888 from patricktokeeffe/patch-1

Add note about updating system path
get-pip.py option examples

Conflicts:
	docs/installing.rst
break out the examples so we can add a qualifying footnote for --user installs

Conflicts:
	docs/installing.rst
Merge pull request #1944 from qwcode/critical_get-pip_docs

docs for get-pip.py options
Replaces spaces in username.
Merge pull request #1986 from matham/master

Replaces spaces in username.
Revert "Merge pull request #1986 from matham/master"

This reverts commit cb26c0b8cb00d18c75503ce4ee59a95a619e8189, reversing
changes made to bb8c7428ab40dde4af92e696ff518e82e214cd24.
remove InstallRequirement.delete_marker_filename
Merge pull request #2230 from xavfernandez/delete_marker_filename

remove InstallRequirement.delete_marker_filename
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
parse_editable: clarify output

extras and editable_options are two different things
Fix environment extras installation for sdist

use pkg_resources.Distribution.requires instead of
Requirements.requirements to have environment markers parsing for free
It also unifies a little the process for wheel and non-wheel installs

closes #2174
drop egg_info_lines

and use pkg_resources.Distribution instead
switch extra requirements log to debug
Fix ``pip list`` when there is an invalid PEP 440 version installed
Merge pull request #2153 from xavfernandez/xfernandez/extras_fix

Fix extras_require and environment markers in sdist
Update changelog
Merge pull request #2236 from dstufft/fix-pip-list-invalid-version

Fix ``pip list`` when there is an invalid PEP 440 version installed
Split up Secure vs Insecure for the requests HTTPAdapters