Merge pull request #66 from groessler/something_to_pull

New src/Makefile variables: USER_CFLAGS and PROGEXT
Moved USER_CFLAGS to the other flags.
Made the CBM stdin consoles echo '\n' to the screen.

That fix makes Commodore platforms be consistent with other platforms' consoles.
Avoided a reload by using a second register.
Added a simplistic read() that gives a stdin console on the Atmos.
Moved the command-line arguments out of BASIC's input buffer.

The stdin console re-uses that buffer.
Reset the stdin console when a program starts.
Merge pull request #68 from greg-king5/line

Add a stdin console to the Atmos target.
Merge pull request #67 from greg-king5/echo

CBM stdin Console RETURN-key Echo
Use deferred VBI instead of immediate VBI. A deferred VBI won't be
called if the user program has interrupts disabled which makes it
easier to avoid race conditions.
Add "joystick mouse" driver and default mouse callback routine (not
using P/M graphics).
fix typo
Add drivers for ST mouse, Amiga mouse, and Atari trakball. Access
routines taken from old mouse.s.
When disabling interrupts, restore original interrupt flag afterwards.