Added interpolateSelector option

[alvarotrigo]

Fixing problems reported in https://github.com/claudetech/node-static-i18n/issues and https://github.com/claudetech/node-static-i18n/issues/15

It allows to do something like:

<div data-t-interpolate data-t>
    {{Download}} <a href="whate">whatever</a> {{file}}
</div>

As well as use indentation such as

<div data-t-interpolate data-t>
    {{Download}} 
</div>

Or translating text without direct wrapper:

<div class="demo" data-t-interpolate>
    <div class="loading"></div>
    {{My text here}}
</div>

[danhper]

Great, thank you!

[danhper]

I just published a new version to npm, thanks again!