Reduce missed Frequency updates, reduce mutex locks, update docs

[theckman]

This change is a small update to help make the spinner a bit more robust.

The first increases internal channel buffer size for frequency updates, to hopefully non-blocking write dropping an update. The buffer size increase is arbitrary, and calling .Frequency() in a hot loop could still result in dropped updates.

The second is the removal of a mutex lock within the Status() method, and an unnecessary nil check. There is not a need for either of them based on how the *Spinner is constructed.

The third is some refinemennt of the documentation both in comments on exported identifiers, and comments within the source code.

[codecov[bot]]

Codecov Report

Merging #43 (8153131) into master (fb3269b) will decrease coverage by 0.01%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #43      +/-   ##
==========================================
- Coverage   94.43%   94.42%   -0.02%     
==========================================
  Files           2        2              
  Lines         521      520       -1     
==========================================
- Hits          492      491       -1     
  Misses         15       15              
  Partials       14       14              

Flag	Coverage Δ
unittests	94.42% <100.00%> (-0.02%)	:arrow_down:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
spinner.go	94.24% <100.00%> (-0.02%)	:arrow_down:

---

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 fb3269b...8153131. Read the comment docs.

[theckman]

@codecov can't do math. This build is fine.