Docs: Addresses explanation

[Shvandre]

Currently, address types in TON (like addr_std, addr_var) are only described in block.tlb, which may not be clear for ordinary users.

Problem:

• Ordinary users may not understand the distinction between addr_std and addr_var.
• The concept of addr_ext is unclear and undocumented.
• There is no explanation of Anycast, which also might be useful.

[novusnota]

Related to #925 and, partially, #1110.
Depends on #1198 and #1119.

There is no explanation of Anycast, which also might be useful.

Btw, Anycast is mostly ignored, isn't it?

[Shvandre]

Btw, Anycast is mostly ignored, isn't it?

Anycast is ignored in 100% cases for now. (And may never be implemented). But actually for now only way to understand what is anycast is to read whitepaper