* New tutorial on importance sampling with X-PSI

* Removing comments

* Removing uneccessary files

* Fixing Sample file

* Unnecessary transformed files removed.

* Prefixes updated in the new main files. Should still update in the importance sampling notebook too.

* Updating comments in notebook

* Small sentence changes.

* Now non-existing "is_secondary" option changed to is_antiphased in the new examples so that the likelihood checks pass.

* Importance sampling output updated to match exactly what I got by running the example.

The difference to the previous though extremely small.

* Font sizes increased and small fixes.

* Notebook moved from examples to docs.

* Importance Sampling tool example added and import paths generalized.

* Name update in the intro page.

* Name update2.

* Fixing boldface syntax for sphinx

* Small extra space added.

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Co-authored-by: Tuomo Salmi <[email protected]>