Merge pull request #1 from Ferguzz/master

Added support for listing athlete's activities.
Add PR effort id, time and distance to segment summary
JSON tag fix
Add new segment effort properties (PREffortId, Hidden)
Move calories and description from Activity Summary to Detailed
Add 'all efforts' endpoint
Add Upload Create
Rename segment.GetEfforts => ListEfforts

This is to be consistent with the rest of the API. List denotes it
returns an array. Get means it returns one object.
Update readme