Added parameter float_precision to CSV parser

closes #8002.
Just tested it out and got an error: `AssertionError: 2.0 != 1.002004008016032` with `PyOS_string_to_double`. Maybe I'm misusing it--any idea what that could be? (this is 1.002... being interpreted as 2.0, 1.00000 was correctly interpreted as 1.0)