initial implementation for XmlBLOB
adding testcases for XmlBLOB
fixing the previous commit
adding more testcases for XmlBLOB
adding a testcase supporting VirtualXPath
implementing spatialite_init_ex / spatialite_cleanup_ex [thread-safe]
refining spatialite_init_ex / spatialite_cleanup_ex
implementing the internal XmlSchema cache
updating the HTML doc
fixing few typos
Fix linker problem when building without libxml2
Fix bad previous commit.
Fix link type problem for VortialXPath test case when XML not enabled.
Add GEOS init (singleton) suppression for valgrind tests.
Merge in geopackage support (experimental). Off by default - requires --enable-geopackage configure option to turn it on.

There is more work required on this to provide demo programs and documentation for the SQL functions.
fixing few minor glitches and porting the GPKG tests on Windows/MinGW
fixing an issue forbidding all lemon/flex parsers to be effectively reentrant
bug-fixing: 
1) trailing whitespaces removal in parseDbfField() as reported by Filip Arlet
2) RecoverGeometryColumn on legacy DB layout as reported by Peter Aronson (ESRI)
Fix errors in GeoPackage base table construction, as identified by Sandro.

Updates code and tests.
FIx raster_column data insertion.