Ref: #1379
This takes a naive approach to font-width computation, the most compute-intensive part of rendering badges.
1. Add the widths of the individual characters.
- These widths are measured on startup using PDFKit.
2. For each character pair, add a kerning adjustment
- The difference between the width of each character pair, and the sum of the characters' separate widths.
- These are computed for each character pair on startup using PDFKit.
3. For a string with characters outside the printable ASCII character set, fall back to PDFKit.
This branch averaged 0.041 ms in `makeBadge`, compared to 0.144 ms on master, a speedup of 73%. That was on a test of 10,000 consecutive requests (using the `benchmark-performance.sh` script, now checked in).
The speedup applies to badges containing exclusively printable ASCII characters. It wouldn't be as dramatic on non-ASCII text. Though, we could add some frequently used non-ASCII characters to the cached set.
I developed this for #820 to provide the correct cache behavior when a service wants to use custom parameters from the query string.
For safety, only the declared parameters (and the global parameters) are provided to the service. Consequently, failure to declare a parameter results in the parameter not working at all (undesirable, but easy to debug) rather than indeterminate behavior that depends on the cache state (undesirable, but hard to debug).
- Add tests to request-handler to prepare for some tweaks to caching for #820
- Clean up code in request-handler: renames, DRY, arrows, imports
- Allow for clean shutdown of `setInterval` code. This requires the ability to cancel autosaving.
- Upgrade to Mocha 4, and clean up so the process exits on its own (see mochajs/mocha#3044)
- Better encapsulate analytics
