Generate Impromptu paths in constructor.

This allows Impromptu.CONFIG_DIR to be overridden before all of the
other paths are generated.
Merge pull request #59 from Impromptu/path-generation

Generate Impromptu paths in constructor.
Rename impromptu.options.prompt to shell
Merge pull request #60 from nb/rename-prompt-impromptu-option-to-shell

Rename impromptu.options.prompt to shell
Rename prompt to shell in CLI. See #60.
Merge pull request #61 from Impromptu/cli-shell-property

Rename prompt to shell in CLI.
Extract parsing the environment into a function

It was getting in the way of reading what the message handler did.
Merge pull request #63 from nb/extract-parsing-the-environment

Extract parsing the environment into a function
Record extra information as environment variables

For now we are adding last exit code and jobs count.

We need to pass these from the shell instance, because they're not
available outside it.
Merge pull request #64 from nb/pass-extra-env-information

Record extra information as environment variables
Bump version to 0.2.3

Changes since 0.2.2:

* Nikolay Bachiyski: Record extra information as environment variables (7c1f44f)
* Nikolay Bachiyski: Extract parsing the environment into a function (2bc73eb)
* Daryl Koopersmith: Rename prompt to shell in CLI. See #60. (fdd8cfc)
* Nikolay Bachiyski: Rename impromptu.options.prompt to shell (133ca23)
* Daryl Koopersmith: Generate Impromptu paths in constructor. (44f8994)
* Daryl Koopersmith: Record prompt errors to a log file. (d53568f)
* Daryl Koopersmith: Handle compiler and runtime errors. (1aac905)
* Mark Jaquith: Tell OS X Terminal about the current directory (d0b85af)
Add the ability to manage and spawn multple prompt servers.
Fall back to the CLI if the server isn't running.
Use IMPROMPTU_DIR to determine location of prompt file.
Update compiled prompt path to use new variable name.
Move test prompt files into their own directory.
Use consistent escape codes in sample prompt test.
Make the config directory an instance-level path.
Expose the test prompt root path.
Add utility to clean prompt directory.