Merge pull request #24 from cefiar/master

Extensive copper thickening (Bug #23).
library update, TL431 symbol and TO92 footprints
RAMPS-FS schematic update: improve thermistor input protection (WIP);
allow external 5V input;
use 220R gate drive resistors on all MOSFETs
Libraries: update with TL431 SOT23;
RAMPS-FD schematic: finish up thermistor protection design; update footprint assignments
RAMPS-FD: update board layout with new thermistor protection (#3, #5);
locking conenctor for EM-STOP (#9);
add external 5V connector (#11)