[info] update version

[info] version bump

[README] release preparations

Merge pull request #516 from jgrewe/invalid_slice

Allow DataViews to become invalid fixes #502

[1.5] release preparations

Version 1.5.0 beta 6

Merge branch 'master' into v1.5

* master: (129 commits)
  [travis] Extra build without compat tests
  Code quality: Remove unnecessary for loop
  Code quality: Remove all unused imports and variables
  TestLinkDimension: Property change tests
  DimensionLink: Write through label and unit
  TestLinkDimension: Remove unnecessary np.app() checks
  Test dimension link index errors
  Index validation for DataArray dimension link
  Index validation for DataFrame dimension link
  Remove AliasRangeDimension and DataFrameDimension
  TestLinkDimension: DataFrame for Range and Set dimensions
  RangeDimension.label: Read through to linked label
  RangeDimension.unit: Read through to linked unit
  Remove unnecessary SampledDimension redirect
  DimensionLink to DataFrame: Apply index to column
  TestLinkDimension: Self link tests
  TestLinkDimension: SetDimension->DA link tests
  SetDimension.labels: Read through to linked data
  Multidimensional indexing should use a tuple
  TestLinkDimension: RangeDimension->DA link tests
  ...

Version: v1.5.0b4

Version bump: v1.5.0b3

Run compatibility tests only when requested

The compatibility tests are no longer run by default when NIX is
detected. They can be run by specifying --nix-compat. If specified, the
tests are compiled and any errors will cause failure of the
compatibility tests. If the option is not specified, the tests are
skipped, even if NIX is available.

One reason for this change is that the compatibility tests were always
compiled when NIX was available, even when they are unselected, and
compilation slows down the tests.

With this change, they are only compiled and run when explicitly
enabled.