Linux doesn't need file extensions since it considers them just part of the file name, Windows depends on them. So to make things simple I think the extensions used by Aurora should be:
.src - a source file
.inc - an include file
.asm - the assembler output file, .a means something else in linux
.lib - A static or inport library on Windows
.a - A library in Linux.
.awp - Auroroa workspace (project file) ?
Looks good to me and makes sense. :)