Add in-line literals for assembler

Now you can use things like %ifoo in .dva files, and it will be
translated to the index of the literal ifoo.
Add in-line literals to disassembler
Add in-line literals to std.dva
Workaround for in-line literals with spaces

v2a.py now simply ignores any literals with embedded spaces.

dvasm.py still cannot handle such literals, and most likely never will.

Note: this goes only for in-line literals. Using the old behaviour of
using numbers in the code section to refer to a specific literal still
works, and since the literal section doesn't split on spaces, you can
still use literal strings with embedded spaces.