added documentation for flags

using scheme-level procedure for raising exception instead of C-level…

… throw_exception [thanks to alicemaz]

renaming db-rm to db-delete as originally proposed; added test case f…

…or db-delete

added srfi-13 to build dep

updated documentation

added new procedures to the documentation

added Caolan to copyright notice in lmdb.scm; set version number to 2.3

Merge branch 'master' of https://github.com/iraikov/chicken-lmdb

search for lmdb in travis file

added mapsize arg to doc