refactor to Compiled.get_params() to return new ClauseParameters object, a more intel...

refactor to Compiled.get_params() to return new ClauseParameters object, a more intelligent bind parameter dictionary that does type conversions late and preserves the unconverted value; used to fix mappers not comparing correct value in post-fetch [ticket:110]
removed pre_exec assertion from oracle/firebird regarding "check for sequence/primary key value"
fix to Unicode type to check for null, fixes [ticket:109]
create_engine() now uses genericized parameters; host/hostname, db/dbname/database, password/passwd, etc. for all engine connections
fix to select([func(column)]) so that it creates a FROM clause to the column's table, fixes [ticket:111]
doc updates for column defaults, indexes, connection pooling, engine params
unit tests for the above bugfixes