The htab_structure has been modified in two ways, which should not break
compatability with any of its uses.
It includes a void pointer, which is in this commit used to point to a
string for defines, and will in the future be used to point to the address
space for words, bytes, and double words.
It now includes a function htab_add_str specifically for storing strings.
It calls htab_add so as not to be redundant, but makes the node's value
their index for the lexer to fetch using htab_find, and assigns their
void pointer.
The lexer will now use htab_find on all tokens to see if they are a define
string, and if so, substitute them with the appropriate token.
The defines htab is destroyed after lexing, because that memory is done.
If the preprocessor encounters a problem, such as failing to load a source
file or an improperly formatted define, it should be able to abort running
the program.
Before allocating space for a token, the lexer will first check to see
if that token is a defined name. If it is, it will allocate space for
the defined string instead.
A test file is included in programs/tinyvm/preprocessor to demonstrate
the behavior. When functioning, the program will print the fibonacci
sequence.
This commit adds behavior to the preprocessor which fills a tree with
defines and their replacements. In future commits, the parser will
substitute instances of the defines with their replacements in the
source code.
