Fixes syntax highlighting

[appascoe]

This resolves #67 .

It appears that using thing-at-point, when looking at the returned properties of the thing would include that the thing was already fontified. This effectively would turn off any syntax highlighting, including the naive highlighting before sclang-class-list is loaded. Switching to another function, current-word, appears to have the correct behavior: when typing out a class, it is not highlighted until the word matches a class in sclang-class-list. For example, starting to type SinOs results in plain text, but upon finishing with SinOsc, it becomes highlighted.