Added a file containing my developer notes.
Added the ability to have a \ escape the LF at the end of a line.

That is
	PRINT("HELLO", \
		"WORLD")
is now a valid statement.
Added some notes, and fixed the test program.
The language is now weakly typed, with & as the string concatenation operator.
Identifiers can still contain $ characters, but you don't need them for string variables any more (there's no distintion between integer and string variables in the language now).
I've also renamed mu_throw_error() to mu_throw()
Minor documentation changes
Made the naming of the interpreter functions more consistent
Changes to the documentation script and some minor documentation fixes.
Fixed the mu_par_num() and mu_par_str() functions to not throw errors anymore if the value is not of the right type. They now silently convert the values. This is more in line with the dynamic typing.
Changed the operation of the VAL() and STR$() built in functions.
The DATA() function now also puts in a x["length"] value in the array.
Subsequent calls to DATA() now appends data rather than replacing it.
DATA() is now also better wrt. the dynamic typing of its parameters.
There is now a new IFF() function that serves the same purpose as ?: in other languages (though the symantics are a bit different).
Added the MAP() built-in function.
Added my test script for the DATA() and MAP() functions.
Removed trailing whitespace from the code.
Added mu_valid_id() to the API.
Fixed MAP()'s documentation.
There is now an expect() function. Jury's still out as to whether it makes the parser more readable.
I've finally added the @ operator for references.
Added PUSH() and POP() functions to simulate local variables.
Added a mu_has_var() API function.