better support for less error messages

[vicapow]

plus unit tests

[techpines]

Yea, I think that is more standard.

[vicapow]

now the message is passed to a new error object. the error message will format an error to look like this:

Less error: missing closing `}`
    filename: syntax-error.less
    line 4 column 0
    ...
     4:   {
     5: }
    ...

[techpines]

Awesome!