feat: new diff mode

[gmickel]

This PR introduces a new improved diff mode for the code modification prompt.

Instead of using the Standard Unified Diff Format, which works fine with Claude 3.5 Sonnet, this PR introduces a diff format more akin to Conflict Markers in Version Control which should be easier for LLMs to output.

This PR also:

• Adds Deepseek API / deepseek-coder support

• Configures the --diff, --no-diff mode automatically based on the selected model. This behaviour can be overriden using the --diff and --no-diff flags.

• the --diff flag is no longer set to be true or false (see above)

• adds the new 'gpt-4o-2024-08-06' version of gpt-4o which is cheaper and has a 4x longer output token limit

• adds a more detailed model recommendation to the README

fixes #84 #85 #87

[github-actions[bot]]

:tada: This issue has been resolved in version 1.14.0 :tada:

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot :package::rocket: