Support user-defined custom tags in `typeMap`

[timkendrick]

I'd love to be able to use gulp-inline to inline different content types based on user-defined tag definitions.

In my case, I need to inline Polymer web component definitions (via <link rel="import"> tags) – but I can see this being really handy for more application-specific use cases (e.g. a custom <i18n key="foo"> tag definition).

Any chance of allowing a custom typeMap to be passed as an option?

[k-funk]

+1ish...

Alternatively, it would be great to target an attribute like href=*.png, or even better, any reference to *.png.

My motivation is because of favicons:

<meta name="msapplication-TileImage" content="/assets/images/branding/favicons/mstile-144x144.png">
<link rel="apple-touch-icon" sizes="152x152" href="/assets/images/branding/favicons/apple-touch-icon-152x152.png">