lldb's history log file is written to at the end of a debugging session.
As a result, the log does not contain commands run during the current
session.

This extends the `fzf_history` to include the output of `session
history`.

Adds a `fzf_history` to the examples directory.

This python command invokes [fzf](https://github.com/junegunn/fzf) to
select from lldb's command history.

Tighter integration is available on macOS, via commands for copy and
paste. The user's chosen history entry back is pasted into the lldb
console (via AppleScript). By pasting it, users have the opportunity to
edit it before running it. This matches how fzf's history search works.

Without copy and paste, the user's chosen history entry is printed to
screen and then run automatically.