add a note about activating hgnested
Merge pull request #56 from hiaselhans/patch_hg

add a note about activating hgnested
minor typos corrected
Merge pull request #57 from kressi/patch-1

minor typos corrected
typo
Merge pull request #58 from udono/patch-1

Fix typo
Merge remote-tracking branch 'upstream/master' into refractor_patch

Conflicts:
	developer_guide/basic_concepts.rst