Merge branch 'develop' of github.com:gertvv/mtc into develop

* 'develop' of github.com:gertvv/mtc:
  Fixes
  Remove unnecessary source()
  Handle continuous data in heterogeneity forest plot
Add arrows when outside range for blobbogram
Always show no-effect line in blobbogram
Slight cleanup 

Signed-off-by: Joël Kuiper <me@joelkuiper.eu>
Slightly better building of arrows

- Remove debug

Signed-off-by: Joël Kuiper <me@joelkuiper.eu>
Merge pull request #55 from joelkuiper/develop

0 always in xrange; arrows when CI outside xrange