Update rtlsdr/rtlsdr.py

Added get and set for frequency correction.
Update README.md

Add frequency correction set example.
Merge pull request #10 from EarToEarOak/master

Added rtlsdr_get_device_usb_strings and library based gain
Merge pull request #12 from EarToEarOak/master

Added get_tuner_type Function
Merge pull request #13 from EarToEarOak/master

Added RTL2832 AGC control
Update rtlsdr.py
Merge pull request #14 from pbutler/patch-1

Fixed bug when bad sample rate is selected.
Merge pull request #17 from EarToEarOak/master

Added set_direct_sampling
add string support for set_direct_sampling()
Merge pull request #18 from superkuh/master

add freq_correction support
add freq_correction property
update README