Allow applications to pass data through resumption tickets and reject early data

[Ralith]

Needed for QUIC and HTTP/3. For example, a prior HTTP/3 session's SETTINGS frame may need to be embedded so that it can be respected in 0-RTT, or serve as grounds to reject 0-RTT if respecting it is impossible.

[coveralls]

Coverage decreased (-0.1%) to 96.388% when pulling 690cb2a on Ralith:resumption-data into 431f42b on ctz:master.

[codecov-io]

Codecov Report

Merging #306 into master will decrease coverage by 0.09%.
The diff coverage is 64%.

@@            Coverage Diff            @@
##           master     #306     +/-   ##
=========================================
- Coverage   96.48%   96.38%   -0.1%     
=========================================
  Files          49       49             
  Lines        8283     8305     +22     
=========================================
+ Hits         7992     8005     +13     
- Misses        291      300      +9

Impacted Files	Coverage Δ
rustls/src/msgs/persist.rs	100% <100%> (ø)	⬆️
rustls/src/server/hs.rs	98.49% <100%> (ø)	⬆️
rustls/src/server/tls13.rs	97.49% <100%> (+0.01%)	⬆️
rustls/src/server/tls12.rs	99.5% <100%> (ø)	⬆️
rustls/src/msgs/persist_test.rs	100% <100%> (ø)	⬆️
rustls/src/server/mod.rs	93.67% <18.18%> (-3.68%)	⬇️

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