Don't diminish subword-mode except in latest Emacs

Closes #138
Change initialisation order for todochiku to better handle missing commands

Fixes #140
Disable slamhound for now, until compatible with cider
Use setq-default rather than setq to configure auto-complete defaults
When ag is available, bind M-? to ag-project globally
Use ruby-mode for .pryrc files
Use conf-mode for foreman's Procfile
Drop visual-regexp package, and use anzu's query-replace functions instead
Remove reference to defunct variable javascript-indent-level
No need to require json package explicitly
Use my new ac-inf-ruby package for auto-complete in inf-ruby
Don't show trailing whitespace in any special-mode
Enable highlight-symbol in prog-mode
Don't suppress ruby-use-smie in Emacs HEAD
Ignore .achievements
Prefer built-in show-paren-mode to mic-paren

In Emacs HEAD, the former works beautifully with SMIE to highlight
blocks, e.g. begin / end blocks in Ruby.
Add note about how to add your own customization

Closes #146
Provide a useful binding of C-c C-z in sql-mode
Use highlight-symbol-mode in html mode too
Save more variables in desktop session file