A new engine process is now started immediately, rather than waiting
until a move needs to be made.
This means that if the engine is playing as black, it can start up
while the human player is making a move. This is noticable with
stockfish, which can be slow to start up.
The GUI now tracks when it becomes disconnected from ChessEngine.
If not currently waiting for a move from ChessEngine, it will
automatically reconnect on the next engine move. If a disconnection
occurs while waiting for a move, the player is asked whether they
want to try again or not.
We have a new, improved string type coming up in AK (OOM aware, no null
state), and while it's going to use UTF-8, the name UTF8String is a
mouthful - so let's free up the String name by renaming the existing
class.
Making the old one have an annoying name will hopefully also help with
quick adoption :^)
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
(...and ASSERT_NOT_REACHED => VERIFY_NOT_REACHED)
Since all of these checks are done in release builds as well,
let's rename them to VERIFY to prevent confusion, as everyone is
used to assertions being compiled out in release.
We can introduce a new ASSERT macro that is specifically for debug
checks, but I'm doing this wholesale conversion first since we've
accumulated thousands of these already, and it's not immediately
obvious which ones are suitable for ASSERT.
