Skip duplicate configurations.

This should resolve #289.

This also detects a bad configuration where multiple blocks attempt to write
to the same destination with different sources.
add suport for block replacement for custom block types
remove self-closing in link tags
fix linebreaks in README.md
Merge pull request #337 from mcampo/custom-types

add suport for block replacement for custom block types
Merge pull request #382 from boushley/skip-duplicates-289

Skip duplicate configurations.
2.3.0
Update README.md
Close GH-360: Update README.md.
Close GH-402: replace data attribute in <object> tag. Fixes #401
Add support for json files
Merge pull request #408 from AlexMeah/master

Add support for json files
Output path respects the hierarchy of the input file. #297