Handle int8/uint8 (and unsigned types on mysql)

Naive handling of int8/uint8 for postgres/sqlite, for Mysql use tinyint/smallint/int/bigint
appropriately, and create the columns as unsigned for Uint8/Uint16/Uint/Uint32/Uint64.
added contributor section to README
Don't create single-used prepared statements for Exec inside a txn
DbMap.Exec - remove commented code (related to #141)
Merge of #127 from @dvander
error instead of panicing in tableFor
#138 - fix spelling of services
Added types for Null* from database/sql

Added types for Null* from database/sql and changed "double" to "real" for postgres val.Name() switch.
#121 - cleanup old Nullable* strings. Use "double precision" for float64 with postgres.
Merge branch 'release/v1.5'
#150 - modify selectVal() to return sql.ErrNoRows, and modify Select* funcs to ignore this error and continue to return zeroVal (per docs).  This fixes SelectOne() for pointers to primitive values.
TestSetUniqueTogether: fix sqlite test expectation (force err string to lower)
Add support for alias column
Modified Pre/Post functions into using interface
Add Pre/Post functions to godoc
Initial test to show failure
This initial test, against this code base, shows that "update" against a
table, with only one column, where that coumn is the primary key, and is
not auto-incrementing, will fail.
Update statements to handle Non-incrementing PK's
The change in this if statement allows for the driver to correctly
handle non-auto-incrementing primary keys. The check has been changed to
if it is auto-incrementing or transient.
Support non-integer autoincrement fields in postgres
Minor documentation clarification
More clarification