Added basic pre-processor support

Tale Jade now has inbuilt support for common pre-processors

You can either use them by using the filter-construct

:less

    p {
        &.red { color: red; }
        &.blue { color: blue; }
    }

or by using import and import-filters or filter-mapping

//Will automatically set the filter to "less"
include my-less-file.less

//or
//will include my-less-file.less automatically
include:less my-less-file

The following pre-processors are now supported:

Markdown

Required Composer Package

erusev/parsedown

Filters

:markdown or :md

Extensions

.md

CoffeeScript

Required Composer Package

coffeescript/coffeescript

Filters

:coffeescript or :coffee

Extensions

.coffee

LESS

Required Composer Package

leafo/lessphp

Filters

:less

Extensions

.less

Stylus

Required Composer Package

neemzy/stylus

Filters

:stylus or :styl

Extensions

.styl

SASS/SCSS

Required Composer Package

leafo/scssphp

Filters

:sass

Extensions

.sass or .scss