Didn't even notice how this was breaking straight-up installations
Merge branch 'devel'

* devel: (133 commits)
  Just a touch-up to this error message.
  Documentation about array methods
  A couple more array methods
  New array methods
  Some improvements to the design of the YTProfile type
  More physical constants
  Remove this commented-out line
  More docs
  Docs for convert_to methods.
  Adding "convert_to" methods which change units in-place
  Actually test both v0.3 and v0.4 on travis
  Get tests working on v0.3
  Changing to reflect installation options
  More fixes for v0.3 compat
  Old syntax for dicts
  Should escape this
  Actually returning what we intended to return
  Should return the actual method or function
  Checking for doc macro
  Relax this requirement--can we support both 0.3 and 0.4?
  ...