[#10,app.yaml][xs]: bump GAE version 4 to reflect switch to dataconverters.
[doc][s]: clean up app.py docstring either deleting or transferring to README.
[#10,app.py][s]: reintroduce tsv support (plus support for encoding parameter).
[#10,xls][s]: re-introduce worksheet argument support.
[#4,xlsx][s]: xlsx support - fixes #4.

Really easy now we have dataconverters and messytables.
[#10,refactor][m]: remove code obsolete transform and brewery code - fixes #10.

Last part of refactor as part of #10 to use dataconverters: remove the old libraries and code we were using.