Remove the internal spacedoc.properties in favor of overridable defaults

[kutis96]

The internal spacedoc.properties is currently not terribly useful, and more relevant defaults should be added anyway.

• Remove internal spacedoc.properties
• Read it by default from current directory, if present?
  • Perhaps from ${pwd}/spacedoc.properties
• Add internal defaults:
  • ffc.polyglot-js = AUTO
    • This option may currently be broken, see Auto-dection of GraalVM doesn't work #6
  • ffc.npx-executable =npx (assume it's on the path)
  • polyglot.js.require.directory =${pwd}/.spacedoc/js/require
  • general.temp-file-prefix = spacedoc-temp
  • general.temp-directory-path = ${pwd}/.spacedoc/temp
• Check for other useful defaults and extend this list.

[kutis96]

This has technically been done in #34, but one should actually check the default values, whether they actually look anything like this.

[kutis96]

Internal defaults can actually be listed now upon runtime, at least in the Markdown module. Use the -PL/--param-use option to list currently used values, including defaults.