Allow using Eval to run Lime tools.

[player-03]

Similar to #1614, but using a different target. This version leaves Neko as the default, but adds Eval as an option. To enable, pass -eval as an argument.

Pros:

• Eval fixes several of Neko's quirks. For instance, it should resolve alloc.c(177) : max_string_size reached #1307.
• There's no need to run lime rebuild tools after each change.

Cons:

• There's a ~2 second pause every time Eval starts up. (I included a message right before the pause to make it easier to measure.)
• CFFI is disabled, which might make some features not work. (But do the tools really use audio and fonts and so on?)
• If someone was already using the -eval flag for their own purposes, this will shadow that. Seems unlikely, given that the usual convention is to use two dashes for any flag longer than a letter.

[player-03]

@AdamHarte Give this one a try, see if it fixes your issue.