Implement remaining statements (last, map, reset, secmark)

[jwhb]

Is your feature request related to a problem? Please describe.
There are some statements that are apparently undocumented but implemented in libnftables-json that are not implemented by this crate.
Some users brought this to our attention: #15 #41 #4 #65.

The following issues may arise:

• panic/error during deserialization when nft json output contains these statements
• user unable to create nftables object with these statements

Describe the solution you'd like

1. Mark crate::stmt::Statement enum as non-exhaustive to avoid breaking changes when new statements are added.
   Originally posted by @JKRhb in Implement SynProxy #29 (comment)
2. Implement remaining statements to be compatible with libnftables-rs.

Describe alternatives you've considered
n/a

Additional context
Missing statements are already marked here.