Readd diesel store and implement the relevant changes

[weiznich]

This readds the diesel store and implements the relevant changes for the expiry PR. Hopefully I've included all removed files. (Next time it might be easier to just leave them in place by just disabling the feature temporary)

[maxcountryman]

How do you want to order merging this with #59?

[codecov[bot]]

Codecov Report

Merging #61 (d54f0ca) into session-expiry (35d560f) will decrease coverage by 0.82%. The diff coverage is 76.47%.

@@                Coverage Diff                 @@
##           session-expiry      #61      +/-   ##
==================================================
- Coverage           80.39%   79.58%   -0.82%     
==================================================
  Files                  13       14       +1     
  Lines                 454      573     +119     
==================================================
+ Hits                  365      456      +91     
- Misses                 89      117      +28     

Files	Coverage Δ
src/lib.rs	7.14% <0.00%> (-1.20%)	:arrow_down:
src/diesel_store.rs	77.77% <77.77%> (ø)

[weiznich]

How do you want to order merging this with https://github.com/maxcountryman/tower-sessions/pull/59?

Merge this and #60 first, and I will rebase #59 afterwards.

[maxcountryman]

This is merged now.