cpu: use bool to represent condition bits
declare register names with enum instead of #define
use uint_t instead of unsigned char everywhere
README: add missing Ubuntu dep: libsdl2-ttf-dev
README: new tested system: armhf raspbian
add pre-created bin/obj/rom directories
update README
load romfiles separately instead of preconcatted
display: emulate cellophane colour overlay
cleanup SDL and free memory on quit
fix segfault and re-enable input handling

I'm stupid... The segfault wasn't in the input handling, it only showed
up there because SDL was intercepting the SIGSEGV.
display: bounds-check writes to pixel buffer
display: better SDL defaults
cpu: bounds-check and mirror memory reads
verify num of bytes read from romfile during init
cpu: eliminate diffs from reference for stackframes
cpu: eliminate diffs from reference for aux carry
update references to project name
cpu: mirror RAM buffer for writes above 0x4000
initialise input struct members to 0