fix (gitClient): trim whitespace when comparing refs

Trim whitespace when comparing hash references. On windows, the refs can
come in with newlines on the end, preventing them from matching when the
should.
docs (readme): add link to windows and linux install instructions
fix (package.json): add sh to postinstall command

Explicitly call postinstall.sh with the sh command to help installations
work on windows.
fix (gitClient): change end of line checks to work on *nix and windows
fix (module): strip whitespace around requested git version

On windows this was not being processed correctly (newlines
left on the end), which was causing the install process to
abort because it didn't find the local version it was looking
for.
fix (install): check for process.getuid before calling it

Process does not have a getuid function on windows. This
simply adds a check for getuid before trying to call it
so this doesn't throw an error on windows.
fix (install): change spawn call on windows

Node on windows has trouble running various things
(npm in this case) inside a spawn call. Details in this issue:
https://github.com/joyent/node/issues/2318

This adds a workaround on windows that calls cmd.exe /C npm
instead of npm directly when trying to `npm install` inside
app modules.

This comes with its own problems -- another problem raised in
that same github issue points out that spawn can leave child
processes running, which, when it happens, ends up preventing
users from deleting the app folder on windows.

If possible, removing the need to npm install here (or replacing
the module system with npm modules) would be a much better long
term solution.
dependencies (npm): update jsio to 2.0.0-beta.5
Merge pull request #36 from gameclosure/feature-windows-support

Feature windows support