Improve documentation for transportation methods

[Floriferous]

When calling /locations, it is unclear what the result will be with multiple transportations params.

For example: /locations ... &transportations[]=ir&transportations[]=ice_tgv_rj Does this return stations that are both of type ir and ice_tgv_rj, or all stations matching any of the 2 ?

It is also not clear what the abbreviations mean, it would be great to add this to the documentation as well for ice_tgv_rj, ec_ic, ir, re_d, s_sn_r, and arz_ext.