Having thread pool as its own singleton in the library meant that each
kiface had its own threadpool, leading to many multiples of the threads
being started. Placing a singleton class in PGM_BASE ensures that all
kifaces use the same thread pool.
The singleton class can be extended to provide single instance
guarantee for any element across kifaces
Recommendation is to avoid using the year nomenclature as this
information is already encoded in the git repo. Avoids needing to
repeatly update.
Also updates AUTHORS.txt from current repo with contributor names
ADDED: Add support in Pcbnew for exporting ODB++ files under Fabrication
Outputs, base on ODB++Design Format Specification (Release v8.1
Update 3 February 2021).
Note: There is still a lot of work to do if we will make the feature as
complete as the ODB++ spec. However, the current functionality's
completeness is already sufficient to cover general production
scenarios. I have compared the output results with Gerber files by
DFM tool and the accuracy at the graphic level should be able to
cover most usage scenarios. Additionally, I am very grateful to
the great open-source project Horizon EDA for giving me a lot of
inspiration in terms of ideas.
The feature can be enabled by adding "EnableODB=1" to the kicad_advanced
configuration file.
Fixes https://gitlab.com/kicad/code/kicad/-/issues/2019
