Added add/remove spelling methods to WritableDatabase

[#13]
Added SPELLING flag to TermGenerator

[#13]
Added QueryParser spelling correction method

[#13]
Doc comment fixes
Added TermGenerator::set_flags

[endlessm/eos-sdk#13]
Changed flag value to 1
Style: horizontal spacing
Added new symbols to doc sections
Corrected query string is now transfer full
Style fixes
Since annotation fixes
XapianTermGenerator:flags property

This adds a GObject property to complement the
xapian_term_generator_set_flags() method. It also adds a default
XAPIAN_TERM_GENERATOR_FEATURE_NONE value to the flags enum.
Merge pull request #14 from endlessm/issues/13

Issues/13