Until now we faked local variables -- they only worked correctly if
there was no overlap between local variables and global variables.
Use a symbol table stack instead of a string list.
Fix bug with looking up undefined symbols.
Document internal CodeGenerator interface
Move license to a separate license file.
Define a public API for calling libacc.
Update the "acc" test program to use the public API.
Move "main.cpp" and test scripts into the tests subdirectory.
Move test data from tests to tests/data
Remove stale test data.
