Added JSON support

Apart from the new "json" format supported by (de)serialize(), this is
sort of a bonus feature resulting from some minor compiler tweaks, making
EEL almost a superset of JSON;

    * Table constructors now support the "fieldName": <value> syntax.

    * The lexer recognizes \uXXXX Unicode escapes.

    * quote() in the strings module now has a flag STRINGS_JSONESCAPES,
      which uses \uXXXX escapes instead of the default non-JSON escapes.

    * The recently added { ... } shorthand syntax for tables.

This allows deserialize() to simply create a constant 'null', and then
compile the JSON input as EEL script!

Added jsontest.eel with JSON data file to the test suite.

NOTE: The \uXXXX escapes do not yet implement full Unicode support; only
      ASCII and the C0 and C1 control code ranges.

Closes #62.
Added vector_u32 and vector_s32 support to the "bin" serialize format