compiler: introduce `wrap` option
compiler: introduce `wrap` option

When present - resulting function will be exported to the `global` or
`exports` object using provided `exportName` or `'BEMHTML'` as a
property name.

fix #7

awinogradov/bem-xjst,mishanga/bem-xjst,awinogradov/bem-xjst,awinogradov/bem-xjst