Re-write "Compatibility with FunC" page of the Book

[novusnota]

In particular:

1. Poor formatting
2. Incomplete examples
3. Exit codes (explain the concept to later be defined by Re-write exit-codes.mdx into an article of the Book #887)
4. Lack of serialization options and details, see Document as bytes32 and as bytes64 #1178 and Document as remaining tact-docs#26

In general, this page and all of the other means for smooth transitioning from FunC to Tact and approaches for integrating existing FunC code to Tact is very important going forward.

Therefore, this page should cover two aspects:

1. Tapping into existing FunC code from Tact — the main focus of this page, for general list of users.
2. Converting FunC code to Tact — for more advanced users. For the most part, this should be covered in "Coming from FunC" page #1130.

Once done, correct existing #-links to that page and add new ones to the appropriate places of the Book

UPD:
Actually, it should just become a part of description for native functions and have its own page similar to upcoming "assembly functions page". There, we'll describe everything people would need or ask when binding to existing FunC code from Tact, plus reference that from the "import code" page.

As for the aspect of converting the FunC code to Tact, it should be covered in #1130.

[novusnota]

Actually, it should just become a part of description for native functions and have its own page similar to upcoming "assembly functions page". There, we'll describe everything people would need or ask when binding to existing FunC code from Tact, plus reference that from the "import code" page.

As for the aspect of converting the FunC code to Tact, it should be covered in #1130.