BUG: fix Wavelet.wavefun() issue.

Introduced in 177a031981.
BUG: accept None input in idwt.  Closes gh-29 and gh-32.
BUG: fix bug in swt().  Introduced in 6eb814c61.  Closes gh-27.
MAINT: fix issue with Travis CI run.
TST: enable test marked as knownfail previously.  Fix was c7447004e70.
TST: fix issue in Wavelet2D node deletion test.

Issue was that the node that was deleted in the test did not yet exist.
BUG: return wavelet properties as string not bytes.  Closes gh-34.
TST: fix test for lazy evaluation of 2-D wavepackets.
MAINT: re-eanble float32 computations through fused types.

This is not faster, need to reconsider later whether this is actually useful.
MAINT: re-enable float32 for upcoef(), downcoef() and swt().
MAINT: make downcoef() accept array_like input.
Merge branch 'enable-float32' into master.

Closes gh-35
Closes gh-9
Merge remote-tracking branch 'upstream/master'