Split pull-request #94 into smaller parts

[Potherca]

Pull request #94 has some nice feature implementations.

In its current state, however, the PR has too many changes to be merged all at once.

To make it possible to split the workload, separate pull-request should be created (based on the code in #94) for the following features:

^{The order of these items is currently semi-random.}

• Add bpkg-logging script
  bpkg_error, bpkg_info, bpkg_message, bpkg_warn are moved from lib/utils/utils.sh
bpkg_debug is newly added
• Add bpkg-utils-url script with generic URL functions.
  I don't think specific functions like bpkg_is_coding_net belong here but that could be discussed.
• Add bpkg uninstall command
• Prefer using BPKG_LOG_LEVEL instead of LOG_LEVEL
• Add Personal Access Token support
• Add BPKG_PKG_PREFIX to overwrite default deps dir

After such changes have been made/merged the remainder of the functionality can be discussed.

To make it clear, all of this does not have to be done by original author. Anyone can pick up (parts of) the workload to move things forward.

[Potherca]

Marked this as completed:

Add BPKG_PKG_PREFIX to overwrite default deps dir

As it has been implemented in v1 as BPKG_DEPS