Prefixed .bash_prompt's functions with prompt_

Refactored .bash_prompt functions to contain the prefix `prompt_`.

This is aimed to increase cosistency throughout the project, along with
all of the variables that already contain the prefix. This will also
help reduce conflicts with shell autocompletion, since all functions
are being exported to the environment and can be invoked from an
interactive shell.
Squashed all but one issue with unexpected PS1
Merge remote-tracking branch 'origin/master' into dev/revive.prefixes

Conflicts:
	.bash_prompt
	test/prompt_test.sh
Fixed up more invocations
Fixed up test script
Renamed everything to sexy_bash_prompt prefix
Updated entire test suite
Fixed up bad name for symbols
Updating documentation with SEXY_BASH_PROMPT_ prefixes
Updated prompt and tests to use PROMPT_ for overrides
Updated override documentation to use PROMPT_
Release 0.24.0