Document programming conventions

[sy2002]

Document programming conventions like INCRB/DECRB in sub-routines and making sure the register bank "pointer" points always to the highest used bank, do not program "look aheads"

R8 as default return value for functions

ISRs must not alter any register (use the stack to save/restore)

sysdef.asm for convenient abbreviations

Monitor "OS" calls

; for comments in assembler
optimal columns (take Q-TRIS as example)

name it best-practices and title it "Programming Conventions and Best-Practices"
TODO: doc/best-practices.md

[sy2002]

Added to scope of issue #28, i.e. release 1.6

[sy2002]

For C: Mention -c99 and -O3 (and that it is worth to use -O3), mention how you can switch to use INCRB/DECRB instead of the stack for functions, mention heap and memory, ...

[sy2002]

We should stick to the 80 character width of ASM source (as shown in Q-TRIS and other code) so that a debugger as described in #66 can display additional information (such as registers) conveniently on the right side without the need of horizontal scrolling (given, that your terminal window is larger than 80 characters).

[sy2002]

First version created.