Log message:
gnuradio-core: update to 3.8.1.0

Here is a very high level list of changes:

## Changed
### Project Scope
- C++11
- merged the wholeness of the `next` branch
- Dependency version bumps: CMake, GCC, MSVC, Swig, Boost
- New dependencies: MPIR/GMP, Qt5, gsm, codec2
- Removed dependencies: libusb, Qt4, CppUnit
- Python: Python 2 & Python 3 compatible. 3.8 will be the last Py2k-compatible
  release series
- gengen was replaced by templates (if you don't know gengen, don't do any
  research; save yourself that sorrow)
- Modern CMake (as far as feasible at this point)
- VOLK version updated to v2.0.0
- .clang-format file now dictates coding style
- clang-format'ed the whole tree.
- installed CMake files now tell about configuration

### gnuradio-runtime
- reworked fractional tag time handling, especially in the context of resamplers

### GRC
- C++ generation as option
- YAML instead of XML
- removed `blks2`
- much better canvas tooling
- consistent gobject usage
- ROUNDED ARROWS

### gr-qtgui
- moving from Qt4 to Qt5

### gr-utils
- `gr_modtool` now vastly improved

### gr-vocoder
- improved versatility
- removed in-tree libgsm, libcodec2, use system-wide libs

## Removed
### Project Scope
- Modules `gr-comedi`, `gr-fcd` and `gr-wxgui` are gone
### gr-comedi
- nobody could remember who used this, or for what. It has seen 0 active code
  contributions in the 3.7 lifecycle
### gr-digital
- python-based `packet_encoder` and related tools: Bugs that were sporadic and
  never fixed, so after long deprecation, we're removing it
### gr-fcd
- since it's currently untestable by the CI, it's being removed, as there was no
  code contributions. Generally, we strive to include all batteries with GNU
  Radio. Re-integration within a more general SDR interface would be desirable.
### gr-utils
- removed PyQwt (dead) based tools
### gr-wxgui
- Unmaintained, breaks on increasingly many systems, always was slower than
  Qtgui. We've been starting to tell people to migrate to Qt since at
  least 2015. Now, we're finally removing it.

Log message:
*: revbump for libsndfile

Log message:
gnuradio-core: use external libvolk. Bump PKGREVISION.

Note that the previous gnuradio-core package conflicts with math/volk.
In order to update you must delete the old gnuradio-core package so
that math/volk can first be installed.

Log message:
Avoid rebuilding everything for doxygen, just the docs are fine. Don't
keep an insanely long hand-maintained list of Python files, go with
wildcards. Simplify various build commands.

Log message:
Fix sphinx name.

Log message:
Fix boost::placeholders fallout

Log message:
Fix boost fallout.

Log message:
revbump after boost update

Log message:
Add missing includes

Log message:
all: migrate several HOMEPAGEs to https

pkglint --only "https instead of http" -r -F

With manual adjustments afterwards since pkglint 19.4.4 fixed a few
indentations in unrelated lines.

This mainly affects projects hosted at SourceForce, as well as
freedesktop.org, CTAN and GNU.