* `build` is an alias which on first use invokes `build-dir --build` to
select a build directory, reconfigure the `build` alias, and invoke
the `build` alias on the selected build directory.
* `debug` is an alias to the installed system native debugger.
* `build-dir` is a function to select a build directory by reconfiguring
the `build` alias, it detects `build.ninja` or `Makefile` in the build
directory and selects the appropriate `ninja` or `make` command.
Depends on the `build-dir.py` Python script which uses the `pick`
package to interactively select the build directory.
* `build-run` is a function which builds the specified target then
attempts to run it, making the assumption it resides in the `bin`
subdirectory of the build directory.
* `build-debug` is a function which build the specified tared then
attempts to debug it using the system native debugger, making the
assumption it resides in the `bin` subdirectory of the build
directory.
