Assembly languages: several fixes and more context highlighting

AVR:

• add _ separator (0b_1100_1111)
• add .directive keywords
• fix @n macro parameter
• fix $abce (hexadecimal number)
• fix preprocessor style
• new style: Branch Instructions, Error, Constant

Nasm:

• fix suffix and prefix number/float (0h11 / 011h, 0xabp2, etc)
• add _ separator (0b_1100_1111)
• fix macro
• fix ..@label
• fix String
• ...
• new style: Branch Instructions, Symbol

Fasm:

• based on latest version of nasm
• more instructions

PicAsm, Dsp56k, M6502, M68K:

• new style: Branch Instructions, ...
• many others changes