Removing code to add a single ssh key if none are provided.

ssh-add, if run without parameters, will add all the keys found in ~/.ssh. There
is no need to use a default file when calling it.
Avoid polluting $error on module load

Closes #116
Use -LiteralPath to handle paths with []

Fixes #119
Reset Get-LocalOrParentPath() checkin name

commit 72fde6f made $pathToTest use Join-Path and in the process dropped the
fullname from $checkin. On my system, this had the negative of introducing as
PS to my prompt when outside of a git repository. Restoring $checkIn.fullname
leaves the path on the prompt an expected c:\path> instead of c:\pathPS>
maybe fix?
Implement describe style setting and functionality.
Fix branch name when in sync with upstream

Fixes #125
Info about trailing exclamation mark

https://github.com/dahlbyk/posh-git/issues/131
Basic support for Pageant as SSH agent

On PowerShell launch, check to see if GIT_SSH exists and is set to
plink. If so, check to see if pageant is running and return if it is.
If pageant is not running, attempt to start it and load all .ppk
files stored in ~/.ssh

Requires pageant to be on path for it to be launched.
Pageant support for Add-SshKey()

Also changes Start-SshAgent() to use Add-SshKey() for both agents.
Add Pageant support to Get-SshAgent()

Also changes gets some information in a more intelligent manner.
Refactor Start-SshAgent code

Make paths for Pageant and ssh-agent more alike.
Add warning to Add-SshKey if Pageant not found
Switch to using -imatch, fix whitespace
Prevent a possible error in Stop-SshAgent
StrictMode support

Change to using Select -ExpandProperty to access properties.
Modif install procedure