Update docs/usage/env.rst

Very minimal word correction
Fix typo in docstring
Adding support to shell_env on Windows. Fixes #804

Windows uses the sintax `SET name="value"` that is almost identical to the Linux counterpart.
Tested on Windows 7.
Fixing the test_use_of_path_appends_by_default
Allow to override 'shell' argument passed to run/sudo in some contrib.files operations
Tweak language of main docstring, update versionadded, re #703
Attribution re #703
Convert to float in case 'wait' was passed in as a string.
Changelog re #791
Merge branch '1.5'

Conflicts:
	docs/changelog.rst
Fix for the 'SSH session not active' exception

Conflicts:
	fabric/state.py
Changelog re #402, fixes #402
Eagerly consume parallel job results.

Should prevent problems where Queue's background pipe fills up
and blocks/hangs. Re #654
Changelog update, fixes #654
Merge branch '1.5'

Conflicts:
	docs/changelog.rst
Merge pull request #797 from nachouve/patch-1

Update docs/usage/env.rst
Update docs/usage/env.rst

Very minimal word correction
Merge branch '1.5'
Merge pull request #801 from tmuellerleile/master

Fix typo in contrib.files.sed docstring
Merge pull request #805 from fgmacedo/patch-1

Adding support to shell_env on Windows