Update low_level_api examples

[SagsMug]

Updates chat example
Updates plain llama example
Adds some usage examples

TODO:

• Test lora

Should fix #141

[SagsMug]

@abetlen I think you can review this now.
I dont really know any lora's, so its left untested
Mirostat was only added to chat, i can add it to the plain example aswell.

[abetlen]

@SagsMug looks good to me, great work.