GRC blocks for rtlsdr

[Peter A. Bigot]

Attached are some custom GRC blocks that might be of interest:

rtl2832-cfile.grc is
http://sdr.osmocom.org/trac/attachment/wiki/rtl-sdr/rtl2832-cfile.grc
updated for the GR 3.7 block locations. Additional changes are setting
Repeat to no on the file source, eliminating the GUI, and adjusting the
bias and divisor to match those used in the current gr-osmosdr RTLSDR
source block.

rtlsdr_file_source.grc is a hierarchical block that combines a File Sink
with the same translation as in rtl2832-cfile.grc so rtl_sdr capture
files can be used without cluttering the layout.

Since grcc has limited support for Parameter block types, for best
results you need to edit the generated rtlsdr_file_source.py.xml to set
the type to file_open. Similarly, edits to both the Python and XML
files are necessary to hook up the file source Repeat parameter.
Examples of these modifications are also attached.

Hope these are useful. If there's a repository they should be
contributed to let me I'd be happy to do that.

Peter