Merge pull request #28 from outbounder/master

simplification and remove of outdated code
Edited concept - mostly reactions

Reactions section is edited to match the reactions library. Requirements (some of them at least) toward reaction implementations are explicitly given.
Merge pull request #29 from vbogdanov/master

Edited concept - mostly reactions
Small fixes, no change in meaning (hopefully)
Merge pull request #30 from vbogdanov/master

Small fixes, no change in meaning (hopefully)
Merge pull request #31 from outbounder/master

add DNA api documentation