Better SyntaxError reporting

[fk-hb]

I use (and love) dotJS in a growing web application.
This morning, I by mistake deleted ':' in "{{##def.myBlock: blah blah #}}". It took me 15 minutes to figure it out!
No clue how easy or hard to put report usefull errors when parsing but it'll be really very helpfull.

[epoberezkin]

duplicate of #56, #122