Added a testing SQLite file

To test functionality, a sample SQLite file that has UTF8 strings in it
has been added and code to get the UTF8 strings was added.
Added properties to show the capabilities

This uses flag enums to show all the possible capabilities. At the
moment these map directly to the GDAL constants pretty much. Might look
at condensing them down if possible, or making them more .NET like.
Added #pragma once to all header files
Updated casing of header includes
Added a string marshaller class to have a single point to convert to/from UTF8 strings coming from GDAL

GDAL assumes all strings a UTF8, but strings in .NET are Unicode, so
these need to be converted in the way in and out.
Allow reading of fields as string.

Started the reading of fields as strings. Will probably implement
IDataRecord on Feature to get all the standard convertions, of which
most will fail due to GDAL not returning data types such as decimal,
etc.