Modify the Lua parser to accept the dual element indexing
Implement bytecode generator rules for matrix indexing expressions
Use explicit LHS rules in bytecode generator
Implement matrix transpose operator using a single quote character

The character is used as a unary postfix operator with higher priority
than any other operator.

Since the single quote is used for the transpose operator the lexer will
accept literal string only with double quotes. This introduce a major
incompatibility with ordinary Lua syntax.
Add missing dependency on lang directory in Makefile
Implement literal matrix literals in parser and AST

Corresponding rule needs to be implemented in bytecode generator.
Implement bytecode generator rule for matrix literals
Add Sublime Text's syntax highlight rules for GSL Shell's language

It is basically a copy of the corresponding Lua files where:
- the single quote string rule is removed
- the single quote character is declared as an operator.

The syntax rules are associated to files with "gs" extension.