6.8.0: Add links to JBJ Playground

Minor changes:

• New documentation, on ReadTheDocs #51
• Better error messages:
  • when mongo is not running
  • when the datapath parameter is forgotten #52
  • homogeneize JBJ errors throwing #56
• Add links to JBJ Playground #62 7f51427 25f64c3 c0dad22

Bug fixes:

• Incomplete loading #46
• Update instance when config is modified #49
• Update instance when files are modified #50
• Pie legend configuration not taken into account when using labels #55
• Dependencies updates, since some were obsolete or security holes (marked, sha1, and qs). See Dependency Status.