Establish versioning convention

[oubiwann]

• There should be a "current" version URL, e.g.: docs.lfe.io/current/
• We should probably follow the LFE release versions, e.g.: docs.lfe.io/v0.9.2/

[yurrriq]

:+1: for current => vX.X.X and for following the vX.X.X convention