Syntax highlighting for the zig programming language

[lordadamson]

[rxi]

Looks good! Two points:

• Can you change the table entry from zig to language_zig to match the plugin name
• The many @... entries (@addWithOverflow and friends) would be better changed to a general pattern that resolves to a symbol, the individual items could then be added to the symbols table instead:

	{ pattern = "@%w+",          type = "symbol"   },