Export Get-SshAgent

Closes #70
updated year on license. aka OCD
changed Add-SshKey to prefer the HOME-EnvVar over the UserFolder ~

OpenSSH and Git uses the folder defined in the HOME Environment Variable, if declared, instead of ~\. Now also Poshgit support these.
Avoid mistaking NuGet for PowerTab

http://stackoverflow.com/questions/13215766/installing-posh-git-in-visual-studio-package-manager
Update prompt to use $pwd.ProviderPath

Suggested by @rpardee (#75)
Update path to TortoiseProc to reflect rename.

TortoiseGit 1.8.0 renamed TortoiseProc to TortoiseGitProc, which caused a
bug in posh-git where calling tgit would throw an exception (could not
find TortoiseProc.exe).

This commit fixes that bug, by testing whether TortoiseGitProc exists and
using that if it does.  If it does not exist, then the default
TortoiseProc is used instead.