MAINT: analog prototypes should return arrays, not lists
MAINT: more helpful error when cheby/ellip called with negative ripple
DOC: Expansion and cleanup of docstrings, add examples
DOC: add note about phase-matched property
DOC: change descriptions of frequency so that rad/s is just an example
DOC: add plt.show() to examples
DOC: Add notes about Thomson Cauer Zolotarev synonyms
DOC: undo Raises section, move butter notes to Notes section
MAINT: filter_design: add missing namespace and consolidate exception messages.
MAINT: combine pre-warp with filter type selection in signal.iirfilter.

Add a fallback for things not implemented, cleanup of pre-warp typo comments,
make pre-warp block the same everywhere, punctuation in error message.
Merge branch 'pr/441' into master.

Reviewed at https://github.com/scipy/scipy/pull/441