Add Member::expelled

[junha1]

/// If true, all voting powers are ignored.
/// Note that once granted, Simperby keeps all members forever in the reserved state.
/// If you want to remove a member, you must set this to true instead of removing the member.
///
/// TODO: consider this in various verification functions.
pub expelled: bool,

[junha1]

Tips

• Write a test case and merge it first
• Take a careful look of verify.rs from the common crate

[sigridjineth]

Check that the version advances correctly.

cc. @yuhatown

struct ReservedState comes from the reserved.rs file. when looking into reserved.rs, finding that the ReservedState struct contains a version is easy one.

Task
Add code to the verify_reserved_state function in verify.rs to check if the current state and the ReservedState version match, but to use semver crate.

 // 2. Check that the version advances correctly.
        if self.reserved_state.version != rs.version {
            if !(self.reserved_state.version < rs.version && verify_version_syntax(&rs.version)) {
                return Err(Error::InvalidArgument(format!("Version advances is incorrect")));
            }
        }

Considering the point where the version of the ReservedState could be arbitrarily changed (but to be included in the git Diff) any block header generated afterwards must adhere to these rules:

1. It must follow the ReservedState.
2. If there's a change, the version must only increment.
3. It should comply with the x.x.x syntax (as per the semver crate).