feat(template): inline SVG headline support

BREAKING CHANGE: Now this framework got even faster, SVG post titles can be inlined in HTML when use `svg-headline`in post front-matter:

```
---
title: Hello World!
category: work
svg-headline: insert_your_SVG_raw_here
svg-headline-width: 400
svg-headline-height: 145
---
```

Note: In most cases, you have to define `svg-headline-width` and `svg-headline-height` in order to make your SVG title responsive to your viewport.