src: tokenize: Rename symbol to token

tests: Generate random locations for symbols ...

This requires adding a new higher-order strategy to set the location of
a symbol.

tokenize: Add locate_symbols function to add symbol locations ...

This isn't the best soltuion yet, but it's a start.

tests: tokenize: Test symbol structure

tokenize: Always specify a location for symbols ...

This gets rid of the default symbol location. The 'default' used now is
just the result of split_symbols.

tests: tokenize: Test location structure ...

I didn't think to test this and it was giving off mutmut errors.
In retrospect it's kind of vital we test the equality check if we're
going to use it to validate tests.

tests: tokenize: Fix test only drawing whitespace

src: tokenize: Use symbol objects for symbols ...

This will be useful for when we add line numbers.

src: tokenize: Don't join whitespaces when splitting ...

This will be useful later when we need to track line numbers.

src: tokenizer: Add beginning of new tokenizer