Update doc site theme

Also:

- Update font files to a much lighter subset versions
- Add headers

doc/config.toml

@@ -74,7 +74,7 @@ disableFastRender = true        # Hugo 0.30
                  , "css/style.css"
                ]
   custom_css_absolute = [ # Iosevka fonts
-                          "https://cdn.rawgit.com/kaushalmodi/iosevka-mirror/v1.13.2/iosevka.css"
+                          "https://cdn.rawgit.com/kaushalmodi/iosevka-mirror/v1.14.1/iosevka.css"
                         ]
   custom_js  = []
 

doc/static/_headers

@@ -0,0 +1,51 @@
+# Paste the below in https://play.netlify.com/headers to test
+# Set max-age to 1 year for stuff not expected to update any time soon.
+/css/*
+  Cache-Control: public, max-age=31536000
+
+/js/*
+  Cache-Control: public, max-age=31536000
+
+/fonts/*
+  Cache-Control: public, max-age=31536000
+
+# Favicons
+/favicon.*
+  Cache-Control: public, max-age=31536000
+/favicon-*.png
+  Cache-Control: public, max-age=31536000
+/mstile-*.png
+  Cache-Control: public, max-age=31536000
+/apple-touch-icon.png
+  Cache-Control: public, max-age=31536000
+/manifest.json
+  Cache-Control: public, max-age=31536000
+
+# Also these images used by the refined theme won't be updated frequently.
+/images/*
+  Cache-Control: public, max-age=31536000
+
+# https://webbkoll.dataskydd.net/en/results?url=https%3A%2F%2Fscripter.co%2F
+# Security Headers: https://securityheaders.com/?q=https%3A%2F%2Fscripter.co&followRedirects=on
+
+## https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Referrer-Policy
+/*
+  Referrer-Policy: same-origin
+
+## https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-Frame-Options
+# I never intend to show any of the pages on my site in a <frame> on my site or
+# elsewhere.
+/*
+  X-Frame-Options: DENY
+
+## https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-XSS-Protection
+/*
+  X-Xss-Protection: 1; mode=block
+
+## https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-Content-Type-Options
+/*
+  X-Content-Type-Options: nosniff
+
+# Content Security Policy
+/*
+  Content-Security-Policy-Report-Only: default-src 'none'; script-src 'self' 'sha256-Zgc2pp+yOmAVogxvTHYBMFKubY0HKk2a0+0+8sX17WY=' https://cdnjs.cloudflare.com/ajax/libs/mathjax/ 'unsafe-inline'; object-src 'none'; style-src 'self' 'unsafe-inline'; img-src 'self' https://*.cloudfront.net https://*.travis-ci.org/kaushalmodi/; font-src 'self' about: data: https://cdnjs.cloudflare.com/ajax/libs/mathjax/ https://cdn.rawgit.com/kaushalmodi/iosevka-mirror/; connect-src 'self'; manifest-src 'self'; media-src 'none'; frame-src 'none'; form-action 'self'; frame-ancestors 'none'; base-uri 'self'; block-all-mixed-content; report-uri https://c571407e2c6d71ed2021633b7fdad0de.report-uri.com/r/d/csp/enforce;

doc/themes/hugo-onyx-theme

@@ -1 +1 @@
-Subproject commit c55002e42b25e2ee8f843bb509bc8cc7046b9e9f
+Subproject commit bfe37f9c9f7281a011c05caccfbb8aa0e4c1276c