Router.update() state option

[caseyWebb]

Support setting the history state atomically, as well as preserve history.state on back button navigation (popstate).

Re: #107

[codecov]

Codecov Report

Merging #108 into master will decrease coverage by 0.1%.
The diff coverage is 50%.

@@            Coverage Diff             @@
##           master     #108      +/-   ##
==========================================
- Coverage   94.51%   94.41%   -0.11%     
==========================================
  Files          42       42              
  Lines         875      877       +2     
  Branches      187      187              
==========================================
+ Hits          827      828       +1     
- Misses         25       26       +1     
  Partials       23       23

Impacted Files	Coverage Δ
packages/router/src/router.ts	86.18% <50%> (-0.49%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 048aa33...ed6875d. Read the comment docs.