[prompt], [fzf] Slightly better support for Unicode-challenged terminals

[Nuru]

what

• Add option to set GEODISIC_PROMPT_GLYPHS to set (or remove) glyphs at end of command line prompt
• Set fzf to use plain ASCII when PROMPT_STYLE is set to plain.

why

Partly address issues such as #417

[Nuru]

@osterman Are you going to fix the lint problem?

[Nuru]

@osterman .travis.yaml explicitly calls make bash/fmt/check, so there is no need for make lint to try to do that as well, so I just took it out. I think the bash/fmt recipes should reference $(CURDIR) rather than $(PWD) but I'm not sure enough about how the whole build system works to make the change right now.