dtype costumization on sql read_table (#8926)

testing dtypes parameter

dtypes defaults to None

dtype type checking and docstrings

dtype exception checking

sphinx dtypes corrections

if/else to or simplification

informative exception of errouneous SQLAlchemy subclassing

type checking

basic documentation of the dtypes feature

issue number

correct test position

issue correction

SQLite dtype configuration

Testing Legagy SQLite with dtype configuration

changed the position of a dtype check

assert_raise

assert_raise

return user specified dtype, not SQL_TYPE

test cleanup

better docstrings

better docstrings

docs and test refactoring

Do not test on MySQL legacy

dtypes->dtype

dtypes->dtype

assert->assertTrue

Type test in mysql

correct mysql test type

reverting unintended change