feat: Simple strings and strings concatenation in bindings

[diosney]

Hi,

First of all, thanks for this library, I'm using your project in a heavy Angular app and its really help towards the reuse the templates for both client- and server-side, a key requirement in my case.

I know that maybe this doesn't make any sense for you, but is a recent need in the templates that I code a binding like:

{{ 'someString' }}

but it seems that the parser does not have support for string detection or not recognize it as a valid scope variable and thus do not print the required string in the resulting compiled HTML.

The ultimate case would be something like:

{{ 'aString_' + someScopeVariable + '_bString' }}

but if the first case worked I would be happy since it a solution to my issue too.

My questions are:

• Are you working regularly on the project so in a couple of days you can take a look in case it is easy for you to add this feature? (of course, if is something that you want to add too).

• If not, please, can you point me in the right direction so I can do it by myself?

Thanks!! Keep the hard work!!