Add NASM (Netwide Assembler) language definition.

This is an update of https://github.com/LeaVerou/prism/pull/365 - see previous PR for discussion.

I have tested this and it works for my files.

Credit to @zeitgeist87 for his help merging the regexes together.
a.k.a. some more of them listed here: http://www.nasm.us/doc/nasmdoci.html
`>`, `<`, `%`, `/`, `=`, `^`, `|`