feat(docs): versioned docs

'versions.txt' contains the available versions one per line.
The json files containing the docs for for each version are stored in
'docs/json/<version>/'.
'npm run docs' creates the json files in docs/json/development,
and version.txt contains the 'development' versions, to allow to serve
the docs locally in an easy way (using for example static).
feat(docs): rename 'development' version 'master'
Merge pull request #220 from silvolu/versioned-docs

feat(docs): versioned docs