fix command line parameter for avr-size
Make serial work with most chips by default
Added pin mapping list to docs, useful for porting
Refactor config.h to allow defaults for chips/boards with different pin mappings
Merge pull request #229 from 0xPIT/patch-1

fix command line parameter for avr-size
Merge pull request #260 from elmom/master

Thanks for the contribution! Looks good. Will update some of the semantics shortly, but the idea is solid.
Processor-independent pin mapping feature.

- Cleaned up and organized pin mapping concept by @elmom.

- pin_map.h allows for user-supplied pin mapping and port vector
definitions in a centralized file. With more processor types, more
definitions could be added.
Pin map definition cleanup.