Linter will check packages submitted for CI build. If error was found,
build will not be allowed.
To ensure that all build.sh scripts are consistent and have at least
minimal allowed quality, linter is permanently enabled for all branches
and pull requests.
Do not use pipes for building & uploading packages because:
* They spawn more jobs on Bintray for metadata generation - each upload is
done in a separate session.
* Bintray doesn't handle well concurrent uploads and metadata can be corrupted.
This happened in all recent builds of platform independent packages - in
each upload task file had a same name and that triggered problem with metadata.
* Using delays for workaround for a problem described above works, but isn't
safe.
* Move package building/uploading implementation from config to a separate script.
* Implement new tag '%ci:no-build' to allow immediately stop build with status 'passed'.
%ci:no-build
These values are not sensitive data.
Also encryption of these values have side effect when they are same as part of
log output: e.g. word "termux-licenses" will become "SECRET-licenses" which may be confusing.
Cache instructions will query system to check if existing cache is available.
While cache will unlikely to be available in build task, it is better to
make it queried before build so if cache folder appear, it will be deleted by
`rm -rf "debs-${TERMUX_ARCH}"`.
