* Remove deprecated PanicXXX functions from codebase
As per discussion over
[here](https://github.com/tendermint/tendermint/pull/3456#discussion_r278423492),
we need to remove these `PanicXXX` functions and eliminate our
dependence on them. In this PR, each and every `PanicXXX` function call
is replaced with a simple `panic` call.
* add a changelog entry
* types.NewCommit
* use types.NewCommit everywhere
* fix log in unsafe_reset
* memoize height and round in constructor
* notes about deprecating toVote
* bring back memoizeHeightRound
* types: memoize height/round in commit instead of first vote
* types: commit.ValidateBasic in VerifyCommit
* types: new CommitSig alias for Vote
In preparation for reducing the redundancy in Commits, we introduce the
CommitSig as an alias for Vote. This is non-breaking on the protocol,
and minor breaking on the Go API, as Commit now contains a list of
CommitSig instead of Vote.
* remove dependence on ToVote
* update some comments
* fix tests
* fix tests
* fixes from review
* WIP: switching to fixed offsets for SignBytes
* add version field to sign bytes and update order
* more comments on test-cases and add a tc with a chainID
* remove amino:"write_empty" tag
- it doesn't affect if default fixed size fields ((u)int64) are
written or not
- add comment about int->int64 casting
* update CHANGELOG_PENDING
* update documentation
* add back link to issue #1622 in documentation
* remove JSON tags and add (failing test-case)
* fix failing test
* update test-vectors due to added `Type` field
* change Type field from string to byte and add new type alias
- SignedMsgType replaces VoteTypePrevote, VoteTypePrecommit and adds new
ProposalType to separate votes from proposal when signed
- update test-vectors
* fix remains from rebasing
* use SignMessageType instead of byte everywhere
* fixes from review
* use increment and decrement operators.
* remove unnecessary else branches.
* fix package comment with leading space.
* fix receiver names.
* fix error strings.
* remove omittable code.
* remove redundant return statement.
* Revert changes (code is generated.)
* use cfg as receiver name for all config-related types.
* use lsi as the receiver name for the LastSignedInfo type.