Document the (complete) grammar inside the specification #84

This issue tracks the work in documenting the grammar.

Since the grammar is very incomplete and I'm willing to complete it, I thought it would be better to do this inside the reference, alongside each item of the language.

Progress:

• Create a script to join the scattered grammar in one place.
• Lexical productions
  • Keywords PR Added keywords grammar #97
  • Identifiers PR Added identifiers grammar #89
  • Comments PR Added grammar of comments #85
  • Literals
    • Char PR Add grammar for char, string, byte, and raw literals #121
    • String PR Add grammar for char, string, byte, and raw literals #121
    • Raw string PR Add grammar for char, string, byte, and raw literals #121
    • Byte PR Add grammar for char, string, byte, and raw literals #121
    • Byte string PR Add grammar for char, string, byte, and raw literals #121
    • Raw byte string PR Add grammar for char, string, byte, and raw literals #121
    • Integer PR Add integer literal's grammar #108
    • Float PR Add float literal's grammar #109
    • Bools PR Add boolean literal's grammar #110
  • Symbols draft
  • Paths draft
• Syntax productions
  • Crates PR Added crates grammar #87
  • Items
    • Visibility PR Added visibility grammar #90
    • Modules PR Modules grammar #143
    • Extern crate PR Extern crate grammar #144
    • Use declaration PR Use declaration grammar #145
    • Static item
    • Const value
    • Functions draft
    • Type aliases
    • Enums
    • Structs
    • Unions
    • Extern blocks
    • Traits draft
    • Implementations draft
    • Const functions
    • Extern functions
  • Attributes PR Added attributes grammar #88
  • Statements
    • Item declarations
    • let statements
    • Expression statements
  • Expressions draft
    • Literal Literal expression grammar #138
    • Path
    • Tuple
    • Struct
    • EnumerationVariant
    • Block Blocks grammar #136
    • Method call
    • Field access Field access grammar #158
    • Tuple indexing
    • Call expression Call expression grammar #134
    • Closure Closures grammar #135
    • Array expression Array and indexing grammar #133
    • Indexing expression Array and indexing grammar #133
    • Range expression Range expressions grammar #142
    • Operator expression Operator expressions grammar #141
      • borrow
      • dereference
      • error propagation
      • negation
      • arithmetic and logical
      • comparison
      • lazy boolean
      • typecast
      • assignment
      • compound assignment
    • Grouped expression Operator expressions grammar #141
    • Loop expressions Loops grammar #139
      • loop
      • while
      • while let
      • for
      • break
      • continue
    • if If and if let grammar #137
    • If let If and if let grammar #137
    • match
    • return Return expression grammar #140
  • Patterns draft
    • Wildcard
    • Reference
    • Struct
    • TupleStruct
    • Tuple
    • Slice
    • Identifier
    • Path
    • Literal
    • Range
    • Box
  • Types
    • path type
    • qualified path type
    • tuple type
    • array type
    • slice type
    • reference type
    • inferred type
    • raw pointer type
    • function pointer type
    • trait object type
    • impl trait type
    • never type (divergent functions)
    • parenthesized type
  • Macros
    • Macro definitions
    • Macro invocations (and the places they can appear, scattered in other grammar items)