smaller code size

most features working:

• time display/set (12/24 hour modes)
• date display/set (with reversible MM/YY, YY/MM display)
• day of week
• seconds display/reset
• display auto-dim
• temperature display in C or F (with user-defined offset adjustment)
• alarm

code size reduced below 4k - no eeprom needed for this build
thanks to @jjmz, @darinfranklin, @ruthsarian, @tux75at, @aFewBits, et al

for STC15W40xAS variants, be sure to pass:
STCGALPROT="stc15" make flash

Note this may not work on all hardware types. Some hardware variations would need to be built manually with options. (No multi-hw building yet...)