Step 1 of removing abseil from lokinet.
For the most part this is a drop-in replacement, but there are also a
few changes here to the JSONRPC layer that were needed to work around
current gcc 10 dev snapshot:
- JSONRPC returns a json now instead of an optional<json>. It doesn't
make any sense to have a json rpc call that just closes the connection
with returning anything. Invoked functions can return a null (default
constructed) result now if they don't have anything to return (such a
null value won't be added as "result").
This rewrites the version info using lokid's approach of compiling it
into a .cpp file that gets generated as part of the build (*not* during
the configure stage).
Among other things, this means that changing the version no longer
invalidates ccache or cmake dependencies, and because it depends on
`.git/index` git commits will cause the version to be regenerated,
making the commit tag more reliable (currently if you rebuild without
running cmake your git commit tag doesn't update).
This commit refactors functionality from the Router class into separate,
dedicated classes.
There are a few behavior changes that came as a result of discussion on
what the correct behavior should be.
In addition, many things Router was previously doing can now be provided
callback functions to alert the calling point when the asynchronous
action completes, successfully or otherwise.
* Import cxxopts to replace getopts usage
* Add visual studio build things
* Fixup abseil build parts
* Replace __attribute__((unused)) with ABSL_ATTRIBUTE_UNUSED
* Fixup minor windows build issues
* Replace getopts usage
* Temporarily fixup .rc files
* More minor windows fixes
* Get a working build
* Revert .rc files
* Revert changes to nodedb
