This commit is multi-fold as it also refactors internally context and logger
as interfaces so it is easier to plug luet as a library externally.
Introduces a garbage collector (related to #227) but doesn't handle yet
parallelism.
Closes#265
It holds necessary state plus additional information relative to the
context which we are being run to (e.g. if we are in a terminal or not).
Besides in the future we can use it also as a contextual logger to
provide more smart logging capabilities.
This also replace the general global configuration instance that
previously was share between the core components.
The realtime output could be configured through
LUET_GENERAL__SHOW_BUILD_OUTPUT environment
variable or related config option or through
`--live-output` option.
