Removed meaningless '~=' operator.

- [ This commit is part of a larger script engine related update ]
- Since: c18f438

Signed-off-by: Haru <haru@dotalux.com>
Added pre de/increment operators. Fixed post de/increment operators.

- [ This commit is part of a larger script engine related update ]
- Suffix ++ and -- operators now behave like in other languages
  (updating the variable *after* its value is returned.)
- Prefix ++ and -- operators are added for parity with other
  scripting/programming languages. They update the variable they're
  applied to *before* returning its value.
- Please note that the implementation of the prefix form of those
  operators (like it happens in most languages) is more efficient than
  the suffix form. '++.@i' is (slightly) faster than '.@i++', or at
  least not slower.
- Fixed some outdated script debug functions.
- Follow-up to c18f438.

Signed-off-by: Haru <haru@dotalux.com>
Corrected operator precedence table.

- [ This commit is part of a larger script engine related update ]
- Operator precedence rules now closely follow those of languages such
  as C and derivates/related (C++, Java, PHP, etc.)
- Please note that if you had custom scripts with non parenthesized
  expressions containing bitwise |, &, ^ operators, they may behave
  incorrectly now (or perhaps they were already behaving incorrectly,
  since the previous behavior was undocumented).
- Added an up to date operator precedence/associativity table in the
  script documentation.
- Added an operator/keyword self-test script in the npc/custom folder,
  in case if may be of some use for future regression-testing.
Added support for automatic concatenation of adjacent string literals

- [ This commit is part of a larger script engine related update ]
- Adjacent string literals are now automatically concatenated into one
  string upon parsing.
- Adjacent string literals are string literals (i.e. "such as this",
  with only whitespace (including line breaks and/or comments) between
  them. For example, the lines:

mes "this will be concatenated " /* skipping this
              comment */ " into one string"; // at parse time

will produce an output of "this will be concatenated into one string".

- The feature brings parity with other languages (i.e. C), and makes it
  easier to split long strings in multiple lines, without having to
  resort to a, slower, run-time string concatenation operator ('+')
- Special thanks to Trojal for the idea.

Signed-off-by: Haru <haru@dotalux.com>