DWDS/Dialing Concordance Code

+ more v2.1.15 comment fixes

* changed default EMA delays to 5,15,60 minutes (after some gnuplot simulations)

* added query language comment support, documented
- C-Style /*...*/ and //..."\n" lexer comments (ignored by lexer; not recoverable from parsed query)
- DDC-style pseudo flag #COMMENT '...', #COMMENT['...']: recoverable from parsed query, but content must be escaped as a symbol

* new class DDCTimeAvg in CommonLib/ddcTime.(h|cpp)
- load-average style exponential moving average with delays of 5,30,60 minutes
- updated CDDCServerStats to use new DDCTimeAvg for average query times (qtavgs)
- makes ddc_server.opt option "StatsWindow" obsolete (documented, now emits warning)
* differentiated "expand_terms" (xtavgs) from "proper" queries (qtavgs) for server stats

+ added jemalloc follow-up observations to change-log

2018-08-21 added new command-line utility ddc_split, using ConcordLib/ConcordSplit.cpp
- partition a single physical index into N subcorpora of roughly equal size
- as for ddc_union, user can also specifiy a target *.opt file to select specific indices and/or bibl attributes for output

+ removed old binary ConcordUnion stuff
+ added ddc_split (guts still todo)

+ ddc_union: sanity checks for bibl constants

+ ddc_union tweaks for translation maps (use vector instead of map)

v2.1.15-pre1:
* 2018-08-17 added new command-line utility ddc_union
- based loosely on old ConcordUnion.cpp code (and the code it calls)
- ConcordUnion.cpp & friends supported only binary union operations, and no option-modification (e.g. MaxTokenCountInOnePeriod)
- new code supports n-ary union including option update and target attribute selection (via -O option)
- old code was apparently never called (and was broken in some places), and should probably go away now