Introduced template terms, refactored some signatures of public API

[Damtev]

Improvements:

• Used a better default value for the Term#isUnifiableWith method - with a javaClass equality, that simplifies introducing new custom terms as sealed classes.
• Introduced a few template terms - EmptyTerm, UnaryTerm, and BinaryTerm, that simplify introducing new custom terms.

Breaking changes in public API:

• Signatures of conde and and are changed not to allow passing empty arguments.
• Methods nil and of in the RecursiveStream are renamed to nilStream and streamOf accordingly.

[Kakadu]

It's funny to look how Kanren's indetifiers become longer and longer, while have a spicial 'to' infix function to create Pairs. From this PR it is not obvious, why this renaming make code more readable.

The changes related to BinaryTerm class are OK

[Damtev]

It's funny to look how Kanren's indetifiers become longer and longer, while have a spicial 'to' infix function to create Pairs. From this PR it is not obvious, why this renaming make code more readable.

The changes related to BinaryTerm class are OK

Just like I said, these changes are introduced to make API more similar to Kotlin standard library