* Move the code for sqlpp::mysql::detail::connection_handle_t to include/sqlpp11/mysql/detail/connection_handle.h
* Move the code for sqlpp::mysql::detail::prepared_statement_handle_t to include/sqlpp11/mysql/detail/prepared_statement_handle.h
* Move the code for sqlpp::mysql::detail::result_handle to include/sqlpp11/mysql/detail/result_handle.h
* Rename sqlpp::mysql::detail::connection_handle_t -> sqlpp::mysql::detail::connection_handle
* Rename sqlpp::mysql::serializer_t -> sqlpp::mysql::context_t
* Add const qualifiers to sqlpp::mysql::context_t::escape() and its parameter.
* Rename class/struct types, variables and functions from CamelCase to snake_case.
* Remove a superfluous function that forwards the call to mysql_close().
* value: add missing includes
* mysql, sqlite3: use explicitly *out* stringstreams for serialization
* postgresql: fix: use max_digits10 instead of digits10
* detail: add float_safe_ostringstream, ensuring floats are serialized with enough precision
* mysql, postgresql, sqlite3, tests: fix: set float-precision for all streams
* run clang-format on changed files
* inline remove_cvref.h
* replace unspecific "wrapper" with concrete type name
* tests: split connector specific tests out of serialize/Float
