New data-cleaning features, Windows mlr.exe, limited localtime support, and bugfixes

Features:

• The new clean-whitespace verb resolves #190 from @aborruso. Along with the new functions strip, lstrip, rstrip, collapse_whitespace, and clean_whitespace, there is now both coarse-grained and fine-grained control over whitespace within field names and/or values. See the linked-to documentation for examples.

• The new altkv verb resolves #184 which was originally opened via an email request. This supports mapping value-lists such as a,b,c,d to alternating key-value pairs such as a=b,c=d.

• The new fill-down verb resolves #189 by @aborruso. See the linked-to documentation for examples.

• The uniq verb now has a uniq -a which resolves #168 from @sjackman.

• The new regextract and regextract_or_else functions resolve #183 by @aborruso.

• The new ssub function arises from #171 by @dohse, as a simplified way to avoid escaping characters which are special to regular-expression parsers.

• There are new localtime functions in response to #170 by @sitaramc. However note that as discussed on #170 these do not undo one another in all circumstances. This is a non-issue for timezones which do not do DST. Otherwise, please use with disclaimers: localdate, localtime2sec, sec2localdate, sec2localtime, strftime_local, and strptime_local.

Builds:

• Windows build-artifacts are now available in Appveyor at https://ci.appveyor.com/project/johnkerl/miller/build/artifacts, and will be attached to this and future releases. This resolves #167, #148, and #109.

• Travis builds at https://travis-ci.org/johnkerl/miller/builds now run on OSX as well as Linux.

• An Ubuntu 17 build issue was fixed by @singalen on #164.

Documentation:

• put/filter documentation was confusing as reported by @NikosAlexandris on #169.

• The new FAQ entry http://johnkerl.org/miller-releases/miller-head/doc/faq.html#How_to_rectangularize_after_joins_with_unpaired? resolves #193 by @aborruso.

• The new cookbook entry http://johnkerl.org/miller/doc/cookbook.html#Options_for_dealing_with_duplicate_rows arises from #168 from @sjackman.

• The unsparsify documentation had some words missing as reported by @tst2005 on #194.

• There was a typo in the cookpage page http://johnkerl.org/miller/doc/cookbook.html#Full_field_renames_and_reassigns as fixed by @tst2005 in #192.

Bugfixes:

• There was a memory leak for TSV-format files only as reported by @treynr on #181.

• Dollar sign in regular expressions were not being escaped properly as reported by @dohse on #171.