Fix typo.
Add null check to avoid polluting $error.
Add installation script.
Merge branch 'master' of https://github.com/lzybkr/TabExpansionPlusPlus
Update installation instructions.
Fix Register-ArgumentCompleter to work with dynamically created script blocks so that they can access functions like New-CompletionResult.
Fix to avoid polluting $error on missing modules.

When a completer has a script block to determine
the commands to register for, the script block
might not find any commands, in which case we'd
try to register a completer with $null for the
command name and that's not allowed.

Fix is to skip registering anything in this case.
Merge remote-tracking branch 'upstream/master'