Merge pull request #515 from astrofrog/revert-travis-numpy

Remove temporary fix from .travis.yml once Numpy builds out of the box on Python 3 on Travis
Added entries in CHANGELOG for units, quantities, and related changes.
Change default value of `relax` to True for reading.
Merge pull request #581 from iguananaut/fits-merge

Fits merge
Make default for writing WCS headers be WCSHDO_safe
Merge pull request #577 from iguananaut/release-tweaks

Release tweaks
Merge pull request #564 from eteq/quantity/allow-arrays

Allow arrays in Quantity
added __float__, __int__, and __long__ to Quantity
added tests for numerical conversion
fix test typo pointed out by @zblz
Added useful error to specifically report that non-scalar Quantities cannot be converted to scalars
Add tests for numerical converters with arrays
Merge pull request #578 from iguananaut/whatsnew

Add a 'what's new' section to the documentation
Preparing release 0.2b1
Back to development: 0.2
Merge pull request #528 from eteq/quantity-add-numerical-converters

Add numerical converters to Quantity
Change implementation of TimeFromEpoch to support all scales

The original TimeFromEpoch (base class for 'cxcsec' and 'unix' formats)
required that the scale be TAI.  This caused errors or failure when trying
to convert to a different scale or initializing a new Time from such
a TimeFromEpoch format object.

    t = Time(100.0, format='unix')
    t2 = t.utc  # crash
    t2 = Time(t, format='iso')  # crash

New implementation does on-the-fly conversion to TAI for converting
to and from JD.  This is more expensive but makes these formats work
like any other format and not be restricted to a particular scale.
Eliminate Time._scale attr and always use Time._time.scale via Time.scale property
Add test of initializing with a TimeFromEpoch format Time object
fixes to configuration auto-generating ported from auto-generate-config branch