Dependency on time 0.3.5 conflicts with requirements in ibc-rs dependency tree

[mzabaluev]

Version(s) of tendermint-rs: v0.23.x branch pre 0.23.2

What went wrong?

Changes landed in #1036 break the build for ibc-rs because it requires rouille, which pins its dependency on time to =0.3.2: tomaka/rouille#246

De-facto tendermint now requires 0.3.5 though (which erroneously is not what Cargo.toml specifies) due to the API it uses.

Steps to reproduce

Uncomment the patch section in the ibc-rs project's top-level Cargo.toml, change the branch to v0.23.x and try to build.

Definition of "done"

The quickest fix is to remove any use of time API post 0.3.2 and make sure nothing in the project requires a higher version.
Luckily, only some non-essential additions currently require that, which can be undone. I'd like to keep the full API In master, though. ibc-rs would have time to address the dependency problems before switching to that.

[thanethomson]

Can we close this now given that #1048's been merged? Or let me know once you've tested with ibc-rs and feel free to close this.

[mzabaluev]

Still no cigar: I left a couple more checked_add/checked_sub uses in the code. Will fix in another PR.