Consider removing license header from a file

[dmdashenkov]

If a code fragment is not specified, i.e. the whole file is embedded, we should remove the first comment of the file (with respect to the source code language) so that users don't need to specify a without-license fragment in each file.

Also, the capability should be configured at the <?embed-code?> tag level with an attribute.

If the fragment is specified, with a regex or with a #docfragment, no such removal is necessary.