Use TAB constant
Somewhat crappy support for ctrl+r history search

Type something, then hit ctrl+r to cycle through history items
which contain the value.

Misfeatures:

* No prompt indication that search mode is on

* No support for ctrl+g to cancel search

* No editing the search while searching

* Search is case-sensitive
Merge branch 'search-history'
Merge branch 'add-history-completions'