Added cstm_cmt_msg_rules.md and modified resources/diffsense.sh.

[dernDren161]

Relates to: #47

Changes:

• Bring your own prompt support (--byo), compatible with all previous modes.
• byo feature can handle all the relative, absolute and other file paths.
• Falls back to base prompt in case the file is not found, not readable or any other errors.
• Proper error handling with correct message corelation displayed in terminal.
• Added cstm_cmt_msg_rules.md file
• As mentioned in PR we don't support --byo "", --byo= is supported to make things simpler.

The byo feature is compatible with previous version of CLI commands. Example:

1. diffsense --byo=.commitFile.md
2. diffsense --byo=.commitFile.md --verbose
3. diffsense --byo=.commitFile.md --verbose --gpt
4. diffsense --byo=.commitFile.md --verbose --nopopup
5. diffsense --byo=.commitFile.md --verbose --gpt --nopopup [X this is not supported as --nopopup does not have the option to select the model as in our previous cases. Will include this in V2 if needed.]

cc: @eonist

[eonist]

💪 Amazing