Update PR-20 - add improved candidate generation techniques and selector can take best of bread if not self refine is used for text generation

[doxav]

(@allenanie as per your request, I pulled from the main branch to update previous PR @#33 )

Features:

• Improved candidates generation by providing different possible strategies (e.g. self refine, best alternatives, variable temperature)
• Improved default selection strategy by allowing to merge candidates in merging best of N

@allenanie : please check that meta prompts used for sequential improved generation (current_prompt) fits properly within your prompt format (might need to use <<< and >>> for candidate(s) in the prompt to prevent confusions by LLM) and test that reference to previous candidate are properly referenced (candidates[-1], previous_solutions).