minor optimizations
implicit initializations
Merge pull request #1 from duartebarbosa/optimizations

Optimizations
Verified that NULL is a 0 in AVR.
Reapeating Duarte's optimizations in time.c through the rest of the module.
Harmonized style throughout the code.
Substituted SPDT switch for a SPST with a pull-down resistor.
Merge remote-tracking branch 'upstream/master'

Conflicts:
	README.md
	sysmods/time.c
	usermods/example.c
	usermods/example.sch