DWDS/Dialing Concordance Code

+ Changes: documented updated min-compat flag

- added configure.ac check for mmap headers and function -> top-level preprocessor macro DDC_ENABLE_MMAP
+ portability hack: slurp to buffer on ddcMMap::open() if mmap is unavailable
+ added sanity checks and warnings in ConcordOptions.cpp for MemoryMap option in case mmap is unavailable

+ fixed mantis bug #27397 ('daughers over-pruned' error from branch-server for limit=0)

+ updated docs for upcoming v2.1.12 file-format changes

+ updated CHitBorders::CBreakCollection::m_BreakOffsets to use mmap()-able ddcVecFile<CTokenNo>, now wrapped with typedef ddcBreakVector

- updated CHitBorders::m_PageBreaks to use mmap()-able ddcVecFile<CPageNumber>

- updated CConcXml::m_Dates to use mmap()-able ddcVecFile<DWORD>

- added CommonLib/ddcStringEnum.h with template class ddcStringEnum<OffT=DWORD> for mmap()-able string<->integer mappings
- updated CConcXml::CFreeBiblStringIndex::m_Values (now m_ValuesE) to use new ddcStringEnum<> with mmap support
+ file format changed: newline-separated "*._bibl_NAME_strings" is now 2 files
~ "*._bibl_NAME_strings_values": NUL-separated values
~ "*._bibl_NAME_strings_idx" : start offsets in *._bibl_NAME_strings_values indexed by logical ID
+ compatibility hack: old "\n"-sparated "*._bibl_NAME_strings" files can still be read in slurp-mode, but produce a warning

+ *perdiv* seems working (still need to test with ddc_index)
+ started work on StringEnum for *._bibl_ATTR_strings (requires conversion, indexing supprt, updated min-compat)

+ added bibl-strings2indexed.perl: upgrade hack for v2.1.12 MemoryMap option