Update toplevel files.

Integrate old INSTALL into README.md, both files had a lot
of (potential) overlap.

Add template for new entries in NEWS, targetting next release.

Bump version number to 6.99-20211218

Tentatively, with the Github migration and all ongoing code
restructuring, we aim for a version 7.0 release at some point
in the future.

INSTALL

@@ -1,57 +1,4 @@
 Installation Instructions
 *************************
 
-Use `./configure; make all; sudo make install' for Unix-like systems.
-
-Depending on your requirements, the following prerequisites are
-needed:
-
-* libelf including header files (for directly reading ELF files)
-* libusb 0.1 or 1.0 (or compatible), including header files
-* libftdi or libftdi1 (for direct access to FTDI devices)
-* libhidapi or libhid (for access to recent Atmel/Microchip dongles)
-
-If the header and/or library files for one of those are found in
-non-default locations, you can add them to configure, e.g.
-
-`./configure CPPFLAGS=-I/opt/local/include LDFLAGS=-L/opt/local/lib'
-
-as an example for MacOS using Macports.  MacOS Brew requires
-
-`./configure CPPFLAGS=-I/usr/local/include LDFLAGS=-L/usr/local/Cellar'
-
-instead. (LDFLAGS and CPPFLAGS can also be supplied as environment
-variables to configure.)
-
-At the end of the configure script, a configuration summary is issued,
-like this:
-
-Configuration summary:
-----------------------
-DO HAVE    libelf
-DO HAVE    libusb
-DO HAVE    libusb_1_0
-DO HAVE    libftdi1
-DON'T HAVE libftdi
-DON'T HAVE libhid
-DO HAVE    libhidapi
-DO HAVE    pthread
-DISABLED   doc
-DISABLED   parport
-DISABLED   linuxgpio
-DISABLED   linuxspi
-
-Make sure all the features you are interested in have been found.
-
-For BSD-like systems, using GNU make (gmake) is not mandatory but
-appears to cause less troubles with the quite complex dependency graph
-that might be produced by autoconf/automake.
-
-For Windows, right now, a toolset like MinGW is required to compile
-AVRDUDE.
-
-Obviously, a working C compiler is needed. Tested compilers so far
-include GCC (in various versions) and Clang. The compiler needs to
-support (at least) C99 language level. For MacOS, either Xcode or the
-(smaller) Xcode Command Line tools are needed, for Windows, some port
-of GCC that supports generating native Windows executables.
+See README.md.