blks2_selector is deprecated - this is a backport for 3.7
from the master branch for 3.8

Also add the callback to the GRC block.

Luzpaz went ahead and found typos using `codespell -q 3`.

This allows users to average per-element.

Might be very useful for spectrum "condensing" and such.

Removed extraneous ')' which waas causing a syntax error in the generated
Python code.

- Add a configurable "file_begin" stream tag
  which is especially useful in repeat mode.
- Added unit tests for new functionality

Propagate_tags -> Propagate Tags
Single key -> Single Key

- Make it possible to specify a single tag key
  to look for instead of all tags.
- Extended unit test for new functionality
- Actually fix a bug which made the unit test do nothing earlier

The tag share block is used to transfer or share tags from one stream to another. The block takes two inputs and one output. The Input 0 stream is propagated to Output 0. In addition, the tags from Input 1 are added to the Input 0 stream. This is useful for transferring a detection tag from a correlate_access_code_bb block to the main complex stream, for example.

The Exponentiate Const Int block takes an integer power of the input complex stream. The exponent parameter must be at least 1. There is also a callback function so the exponent can be changed at runtime.

…tter

…ipulation blocks pdu_filter, pdu_remove, and pdu_set and associated GRC files.

…ple input vector mode. Defaults to off.

Operation unchanged unless enabled by setting vlen_out to be equal to vlen.  Then it does elementwise max/min.

… bindings