Hardware breakpoints are by definition architecture dependant. Move them
off the DebuggedProcess struct and onto the associated arch struct.

Prevents leaving around a bunch of zombie processes

Process is an incorrect name for the DebuggedProcess struct that the
thread is "a part" of. Also, no need to export that field.

Add a test support package which allows shared test functionality
for both the unit and integration tests.

Tests importing the proctl/test package will gain access to a special
test entrypoint which precompiles fixtures and makes them available
to tests.

Add a -headless flag which runs only the debugger server until
a SIGINT is received.

Introduce a client error type which preserves HTTP error information
but which doesn't render the HTTP details by default.

Refactor to introduce client/server separation, including a typed
client API and a HTTP REST server implementation.

Refactor the terminal to be an API consumer.