docs: document milltask's "ini.*" hal pins

Signed-off-by: Jeff Epler <jepler@unpythonic.net>
emccalib.tcl: enable search in POSTGUI_HALFILEs

ini hal pins don't exist when [HAL]HALFILEs are executed
but do exist when [HAL]POSTGUI_HALFILES are executed

also: modify example configs/sim/axis/ini_hal_demo.ini
      to demonstrate ability to use calibration for
      ini hal pins

Signed-off-by: Dewey Garrett <dgarrett@panix.com>
Signed-off-by: Sebastian Kuzminsky <seb@highlab.com>