[FIX] Advances in snp_store adaption to new I/O module.

GFF support works now.
[DOC,FEATURE] Adding documentation built with Sphinx.
[FEATURE] Integrating Disqus into tutorial on readthedocs.org.
[DOC] Adding Dave's fixes and improvements to Sphinx manual.
[DOC] Merging more tutorial updates by Dave.
[DOC] Template updates.
[DOC] Disabling Disqus comments again to see whether they cause problems.
[FIX,DOC] Trying to tackle RTD issue with header/footer injection.
[FIX] Fix for layout.html.
[DOC] Trying to use page.html instead of layout.html...
[DOC] Removing "How To:" prefix in howtos.
[DOC] Fixing foldable spacing in CSS.
[DOC] Hiding genindex and search on start page.
[DOC] Updating requirements of seqansphinx.
[DOC] Adding attic for manual.
[DOC] Bug removal and improvements to the manual.
[DOC] Adding one more fragment link.
[DOC] Adding DOIs for references.
[DOC] Improvents to index.rst

* adding short summary what SeqAn is about
* fixing typo
Merge branch 'feature/stream/develop' of github.com:holtgrewe/seqan into feature/stream/develop

Conflicts:
	core/apps/snp_store/snp_store.cpp
	core/apps/snp_store/snp_store.h