Bug fixes and user issue supports

• add LICENSE file
• fix a memory leak in database ctor
• c++ compatibility (std::iterator and std::tuple)
• add clearing_bindings() in statement (query and commant)
• support nullptr with binder()
• merge the pull request to check nullptr for string value
• add runnable test cases using memory db. test/testdb.cpp

Uses sqlite3_prepare_v2 instead of deprecated sqlite3_prepare

v1.0.8

Adds a section about execute_all.

Support usages in loadable extensions.

See https://sqlite.org/loadext.html for loadable extensions.

Updates version number definitions in header files.

v1.0.6

Update version number definitions.

Support sqlite3 backup API.

Merge pull request #36 from iwongu/backup

Supports backup methods in database class.

Make dtors not throw exceptions.

v1.0.3 has the changes only in headeronly_src. I forgot to update files in src.

Make dtors not throw exceptions.

v1.0.3

Make dtors not throw exceptions.

More helper methods

changes and extended_error_code added in database.

Bug fixes

Fixes #29

v1.0.0

Add version numbers.