return secure context options instead of certs+meta

[msimerson]

• remove enableSNI option
• refactored parse_x509 out of getDir, added tests
• getDir: instead of returning cert & meta, return options block tailored for tls.createSecureContext()
• add getSecureContexts()
• add getSecureContextOptions

WIP, not ready to merge. Yet.

[codecov-io]

Codecov Report

Merging #13 into master will increase coverage by 0.04%. The diff coverage is 88.88%.

@@            Coverage Diff             @@
##           master      #13      +/-   ##
==========================================
+ Coverage   88.21%   88.25%   +0.04%     
==========================================
  Files           1        1              
  Lines         246      281      +35     
  Branches       71       84      +13     
==========================================
+ Hits          217      248      +31     
- Misses         29       33       +4

Impacted Files	Coverage Δ
index.js	88.25% <88.88%> (+0.04%)	:arrow_up:

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[msimerson]

Right idea, wrong place to put the code. A soon-to-land PR moves the TLS config stuff into the one place it can be used everywhere: tls_socket.js. No more of server.js and tls_socket.js reaching back into plugins/tls.js to see how it worked out.