Fix various runtime errors and other miscellaneous things.

Most of these just involve adding `expectConsume` where expressions are expected but a few were slightly different.

16adce3 Previously any expression was allowed on the left side of a bind. I have restricted it to only identifiers and members now which seems to work fine and all the test cases pass, but is this too restrictive?
215c120 These runtime errors only appeared in the command-line version of Minigrace, not the JS interface for some reason.
969330d In light of the recent discussion on Grace naming conventions, I've renamed variables and methods with underscores to use camelCase. Also I removed any trailing whitespace from lines.