join-standalone-tags doesn't follow mustache spec

Hi Felix,

Thanks for making clostache, I've really enjoyed using it!

While tracking down a bug in my code, I realized that partials on their own lines don't save the newline at the end of partial, instead replacing it with whatever the partial contains, and looking through the clostache source, I found join-standalone-tags, which seemed the likely source of this behavior.

The commit messages for that function didn't give a lot of context for why this change was made, but it looks like this no longer follows the mustache spec for partials, which I found here. The overview of the partials spec doesn't define how to handle newlines at the EOL in the case of standalone partials, however, the test for the spec -- line 54 -- shows it as keeping the newlines at the end of standalone partials.

Is this the desired behavior for partials in clostache?

Thank you,
Evan