Firmware progress

I've been making quite a bit of progress with the Lettuce core firmware lately, highlights include:

• Registry - an updatable persistent settings database (stored on EEPROM), which can store data of any type against a key value.
• Expression evaluator - can evaluate simple logic expressions (using AND, OR, NOT) to determine the state of an output based on input values.
• Dynamic memory manager - used to allocate blocks of RAM memory from a heap. This means that plugins can allocate the memory they need on the fly, so we are not restricted to just one plugin of each type.
• SPIMEM manager - used to allocate available memory chips from the SPIMEM plugin.