Setting for selecting `linux-terminal` windows by WM_NAME (window title)

[cdbrendel]

As I proposed in #163, this pull request adds an optional setting window_name that alters the behavior of the linux-terminal prog setting. If set, xdotool will attempt to find a window with a WM_NAME that matches the window_name pattern. If unsuccessful, it will fall back to the default behavior (i.e., just send code to the latest window whose WM_CLASS matches the value of linux_terminal). This pull request also contains a proposed subsection in the readme describing the use-case of window_name and giving an example configuration.

The anticipated user of this setting is someone who simultaneously uses multiple windows that contain multiple REPLs--for example, a researcher or analyst working on a project with a mixed codebase whose workflow consists of running Python code before running some R code to analyze the results. This pull should be particularly useful for users who configure their workspace[s] with saved layouts (in which assigning immutable names to windows is very common). Prior to this pull request, the workaround that I personally used to emulate this behavior was to run different REPLs in different terminal emulators (radian in Terminator, ipython in kitty, etc.).

This is obviously my first pull request for SendCode, so sorry for any silly mistakes or assumptions!

[cdbrendel]

Thanks for reviewing so quickly @randy3k! I agree with all your feedback and I've implemented your suggestions in the latest commits.