megax8: Added a couple of timer modes

Pretty obvious timer modes were missing...

Signed-off-by: Michel Pollet <buserror@gmail.com>
twi: Added first bit of slave support

Need the slave support for TWI, will add bits as I go along

Signed-off-by: Michel Pollet <buserror@gmail.com>
misc: Traces updates

Applies naming convention to globals, types etc.
elf: Redone the symbol loader

Old symbol loader had been geared for the 'trace' functionality, and was
partitularly bad since it didnt know the size of the code it was
loading.

New version loads a (sorted) array of symbols, and let the firmware
loader code deal with the old 'codeline' array. The new loaded symbol
table can be used separately (board code can look into it).

Also changed the avr_symbol_t to inline the symbol name, instead of
using a separate pointer.

Signed-off-by: Michel Pollet <buserror@gmail.com>
twi: Prototype support for slave mode

This is not working fully right now.

Also changed the MOSI/MISO names for the IRQ, as they make no sense when
using the master/slave TWI.

Signed-off-by: Michel Pollet <buserror@gmail.com>