Add templating feature

This is a nice feature that we can build static parts of a PDF file before, save them, and then later on we put them on the dynamic content for everypage. Though the way I implemented it may not be the best(for example you can switch pages, which you should not, or maybe the fonts may not work), but at the moment it basically works:

I added these functions to public API:

 * `startTemp()` -> starts the templating mode

 * `endTemp()` -> ends the templating mode

 * `outputTemp()` -> which will outputs the template

I added an argument to the end of the constructor function:

 * `constructor: (@options = {}, temp)` in which temp is object that is returned by `outputTemp()`

Beside that 3 variables:

 * haveTemp: false

 * isTemp: false

 * temp -> which holds the template object

But this is just a work in progress. I'm thinking of adding features such as, building on a pre-built file, or having multiple templates.