Actually implement configuration options checking

Fixes #1, I guess.
Add docs for configuration options
Handle some edge cases with the cmdline focus handling.

Also silences the unnecessary "No matching autocommands" errors.
Merge.
Fix bad merge.
Added tag v1.0.0 for changeset 0a617f63ae49
Added tag v1.1.0 for changeset 8db3c10cdef0
Update changelog.
support xterm and cursor colors
Added support for future tmux Focus handling

Default cursor escape sequence is now a configuration option

Preserve values of t_ti and t_te to prevent conflicts
Extracted focus handling escape sequences to config

Added configuration to forcibly enable sending iterm focus escape
sequences
Added rxvt perl extension for focus
Enable vitality when iterm_force_focus is set
detect rxvt-unicode and tmux focus support, default escape sequences based on virtual-terminal
Do not wrap focus tracking for tmux

tmux supports this natively now.