Standard token naming convention

[xgreenx]

At the moment the library implements the next standard tokens: ERC20, ERC721, ERC1155.

But naming Erc* is related to the Ethereum network. In the case of Polkadot, we need to define our own specifications.
For specification, we can use PSP repository. Like naming, we can use PSP20 and etc. But maybe someone has better ideas about the naming of tokens.

!ink and Rust have unique features so we also need to think about the optimal function and their signature.
For example, we can include decrease_allowance and increase_allowance to Erc20 implementation like standard functions.

This is is blocker because the naming of traits influences the generation process of selectors for functions. So changing naming of traits later will break cross-contract execution of deployed contracts.

Proposals status:

• Fungible tokens - w3f/PSPs#22 and w3f/PSPs#25
• Not fungible tokens - w3f/PSPs#34 and w3f/PSPs#39
• Multi token - w3f/PSPs#37

[xgreenx]

We created a proposal to define traits for fungible tokens.
When the proposal will be approved we will adopt the implementation and will create proposals for ERC721 and ERC1155.