New Kind in JuliaSyntax module; use @ K_str everywhere

Replace the @ enum-based version of Kind with a custom bits type.
This allows us to use the K_str macro to name the enumerants with more
self-descriptive names.

Refactor to use this new Kind type everywhere from the lexer to the
parser.

Author: c42f

src/JuliaSyntax.jl

@@ -5,6 +5,7 @@ using Mmap
 # Helper utilities
 include("utils.jl")
 
+include("kinds.jl")
 # Lexing uses a significantly modified version of Tokenize.jl
 include("Tokenize/Tokenize.jl")
 using .Tokenize.Tokens: Token