Minor cleanups to coverage info

Added missing "-g" option needed to install istanbul with rpm.  Plus fixed some minor typos
Add --coverage_html support to cli

Enable running $ guard-jasmine --coverage_html to generate the html coverage report.
Bug fix: coverage hangs for large files

The code that used IO.pipe & ChildProcess to run istanbul was waiting for the process to finish before reading the result.  With a file whose instrumentation is large enough to exceed the system IO buffer size, the istanbul process would block and we'd have deadlock.  Rather than fixing that using the appropriate nonblocking reading, just switched to %x[]
Add --coverage_summary to cli
Merge remote-tracking branch 'origin/pr/109'
Merge remote-tracking branch 'origin/pr/110'
Add specs for new CLI options.
Minor whitespace cleanup.
Add new CLI options to the README.
Release 1.12.2