Add "list" command

Build "help" message from command description
Do not throw error when config.json is missing

* Refactor to move some code from Main.hs to Hsbin.hs.
* Remove program name from error message since it is automatically
  added.
Add example config.json
Write hash value as hex string
Add "update" command to compile scripts
Relax lower version of base, support GHC-7.6
Fix typo in help
Add an option to force compile scripts
Create temp subdirectory for each script at build
Add "clean" command to remove old files and directories