Fixed generic clock  bugged on windows

problem : the accumation sometimes accumulate 0 instead of 1 or 2 (cause
the time resolution on windows is not accurate and the refresh is too
speed and the clock is restarted. I fixed that, it's not beautifull but
that's should work.
Merge branch 'master' of https://github.com/Zardoz89/dcpu_vm
Improved assembler, support '+' operator

Now assemble :
- lem_splash.dasm
- hwtest.dasm
- clock.dasm
- lem1803.dasm
- test2.dasm
the syntax of tester.dasm is not correct and will be refused.
gnarfel.dasm/stillalive.dasm have errors... Negatives numbers are not
supported use hexa instead.
Know bugs : ';' in first character of line = error
Merge branch 'master' of https://github.com/Zardoz89/dcpu_vm
Support org and resw symbol for the assembler
Updated doc for the assembler
Spell check
Merge branch 'master' of https://github.com/Zardoz89/dcpu_vm into floppy
Added a option to select a floppy disk image. By default uses disk.dsk