Support for option.alias for define file load path.

[Akimyou]

Usage

// a<!--@include @static.txt-->c
preprocess.preprocess(input, {}, { alias: { '@': 'test/fixtures/include/' } })
preprocess.preprocess(input, {}, { alias: { '@': path.join(__dirname, 'fixtures/include/') } }).should.equal("a!bazqux!c");

Node

Alias value must be a dir path.

Test

Coverage summary before 704d2898

Statements : 96.8% ( 242/250 )
Branches : 86.15% ( 112/130 )
Functions : 100% ( 33/33 )
Lines : 97.57% ( 241/247 )

Coverage summary after

Statements : 96.93% ( 253/261 )
Branches : 86.23% ( 119/138 )
Functions : 100% ( 33/33 )
Lines : 97.67% ( 252/258 )

[coveralls]

Coverage increased (+0.1%) to 97.674% when pulling 6de9b00 on Akimyou:feature/include_alias into 704d289 on jsoverson:master.

[Akimyou]

The same problem !

#127