config

Changes:

• Update configuration file documentation
• Rename .tiorc to .tioconfig, tiorc to config, etc.
• Add support for $HOME/.tioconfig
• Replaces what used to be $HOME/.tiorc
• Fix double prefix key regression

Vyacheslav Patkov:

• Better error checking in config file, rename the file
• Accept true, enable, on, yes, 1 as true values, their counterparts as false ones. Check integer values for errors and range. Warn about ignored (e.g. misspelled) options.
• Check getenv() return value for NULL.
• Rename tiorc to config, as it's a static INI file, not an executable run commands.