Common: Set up command to get subcommands

The command interpreter was updated to allow the commands to get user
input.
Common: Bug fixes to subcommand stuff

Various fixes to get the subcommand stuff working
Common: Fixed argAsInt to handle negative numbers
Common: Allow variable TWI frequency

The config.h file can now be used to set the TWI SCL frequency.
Standalone Timer: Added timing function

Added functions to sort and modify events
Standalone Timer: Fixes for the timing functions
Common: Fixed bugs with command interpreter

Fixed some bugs with the command interpreter. Tested the code with a
meg328p and it seems to work.