BUG: Fix FrozenNDArray & FrozenList string methods

Plus basic tests (i.e., "Hey! If you pass me unicode I don't fail -
yay!")
Merge pull request #4929 from jtratner/fix-repr-on-FrozenNDArray-and-FrozenList

BUG: Fix FrozenNDArray & FrozenList string methods
ENH: Make ExcelWriter & ExcelFile contextmanagers

both can be used in with statements now. Makes it easier to use with
multiple writers, etc.

Plus touch up the docs on writers and such.
DOC: add HTML bad-request cookbook example
Merge pull request #4933 from jtratner/make-ExcelWriter-contextmanager

ENH: Make ExcelWriter & ExcelFile contextmanagers
BUG: Fixed a bug with setting invalid or out-of-range values in indexing
     enlargement scenarios (GH4940)