Add support for CustomError

[montyly]

• Create a new CustomError core object, and associated parsing classes
• Create a specific solidity funciton to handle the revert CustomError
  call
• Fix Custom errors in solidity v0.8.4 cause slither exceptions #919, Fix ParsingError with solidity's custom errors #893

The CI test is currently

pragma solidity ^0.8.4;

struct St{
    uint v;
}

error ErrorSimple();
error ErrorWithArgs(uint, uint);
error ErrorWithStruct(St s);

contract VendingMachine {

    function err0() public {
        revert ErrorSimple();
    }
    function err1() public {
        St memory s;
        revert ErrorWithStruct(s);
    }
    function err2() public{
        revert ErrorWithArgs(10+10, 10);
    }
    function err3() public{
        revert('test');
    }
}

But I want to stress a bit more the parsing before merging the PR

[lgtm-com]

This pull request introduces 2 alerts when merging c8ee69c into 8236010 - view on LGTM.com

new alerts:

• 1 for `__eq__` not overridden when adding attributes
• 1 for Missing call to `__init__` during object initialization

[lgtm-com]

This pull request introduces 2 alerts when merging cc4877e into 8236010 - view on LGTM.com

new alerts:

• 1 for `__eq__` not overridden when adding attributes
• 1 for Missing call to `__init__` during object initialization

[lgtm-com]

This pull request introduces 2 alerts when merging 041f393 into 8236010 - view on LGTM.com

new alerts:

• 1 for `__eq__` not overridden when adding attributes
• 1 for Missing call to `__init__` during object initialization

[lgtm-com]

This pull request introduces 2 alerts when merging 234dcd6 into 8236010 - view on LGTM.com

new alerts:

• 1 for Missing call to `__init__` during object initialization
• 1 for Comparison of identical values

[lgtm-com]

This pull request introduces 1 alert when merging f028c57 into 8236010 - view on LGTM.com

new alerts:

• 1 for Missing call to `__init__` during object initialization

[montyly]

Errors defined within a contract are not yet supported, for example:

contract A{

    error MyError(uint);

}

[lgtm-com]

This pull request introduces 1 alert when merging 2367da7 into a9e9b30 - view on LGTM.com

new alerts:

• 1 for Missing call to `__init__` during object initialization

[lgtm-com]

This pull request introduces 2 alerts when merging 486bc2f into 154dd9f - view on LGTM.com

new alerts:

• 2 for Missing call to `__init__` during object initialization

[lgtm-com]

This pull request introduces 2 alerts when merging 55db069 into 154dd9f - view on LGTM.com

new alerts:

• 2 for Missing call to `__init__` during object initialization

[lgtm-com]

This pull request introduces 2 alerts when merging 0ccde2e into 154dd9f - view on LGTM.com

new alerts:

• 2 for Missing call to `__init__` during object initialization