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
Big ole roadmap overhaul
Add example of `execute` host lookup combo tasks
Add FAQ link & counterexample
Merge branch '1.5'

Conflicts:
	docs/roadmap.rst
Fix a bunch of minor bugs in doc Sphinx formatting
Merge branch '1.5'
ReST fix
Bump dev version
Add env.eagerly_disconnect, fixes #818
Release 1.5.2
Merge branch '1.5'

Conflicts:
	docs/changelog.rst
	fabric/version.py
Add regression test re #581
Merge branch '1.5'
Read system known_hosts file.
Rewrite try/except block in cleaner style.
Updated changelog (for ssh_known_hosts handling).