Change LD_PRELOAD in acc_bash to absolute path.

Relative path leads to libacc_preload failing to be found so change to
absolute path.
Expand and correct build requirements in docs.

- Add Make and Clang requirements.
- Change ZeroMQ from 2.2 to 3.2 as zmq_sendmsg is used which is only found
  in the later version.
- State requirement for development packages of ZeroMQ and LibYAML.
Fix output to avoid extra comma near start of line

- Change json_start to set g_first_node to true so that json_node doesn't
  print a comma for new lines after the first one.
Merge pull request #3 from apel/output_fix

Fix output to avoid extra comma near start of line
Merge pull request #2 from apel/ld_preload_fix

Change LD_PRELOAD in acc_bash to absolute path.
Merge pull request #1 from apel/doc_improvement

Expand and correct build requirements in docs
Merge branch 'dev'