Added theme and template objects.
Theme and Template

Using theme and template to build the prompt.
Caution! Git partial now is broken because Template currently does not
support async partials.
Using theme and template instead of renderer
Using template context instead of builder
Template styles decoupled and expressions parser.

- Decoupled styles from builder to render layer via templates.
- Added an expression parser to the template layer to parse all those
  styles on render time.
Template styles decoupled and expressions parser.

- Decoupled styles from builder to render layer via templates.
- Added an expression parser to the template layer to parse all those
  styles on render time.
Merge branch 'template' of github.com:repejota/bashprompt.js into template

Conflicts:
	lib/theme/template.js
Merge branch 'template'