Proposed backports for time 0.2

[jhpratt]

As time 0.3 is nearing an alpha release, some backports to 0.2 may be desired. This will not lead to the addition of any newly-implemented APIs.

Some things that may be worth backporting:

• Renaming of OffsetDateTime::timestamp{_nanos} to OffsetDateTime::unix_timestamp{_nanos}. The old method names can be deprecated.
• Move macros to macros module
• Deprecate anything that is removed that is not already deprecated
• Remove unused syn/derive feature #291
• Change cfg_attr(tarpaulin, skip) #265 if it's not done already
• The call to localtime_r may be unsound #293

[jhpratt]

All the backports listed above have been completed and released as part of time 0.2.23.