LayoutEngine/Round: use 'roundf' instead of 'ceilf'

This removes wrong calculations for scrollbar's position
due to wrong rounding in Element's SetScrollLeft/Top
Merge pull request #156 from rndfax/master

LayoutEngine/Round: use 'roundf' instead of 'ceilf'
Work around for roundf not being available in VisualStudio prior to version 12.0 (VS2013)
Fix for issue #157 created when PR #156 was merged.
Merge branch 'hotfix/visualstudio-missing-roundf'

Fix for issue #157 created when PR #156 was merged.
Merge branch 'master' into pr-request-made

* master:
  Work around for roundf not being available in VisualStudio prior to version 12.0 (VS2013) Fix for issue #157 created when PR #156 was merged.
  LayoutEngine/Round: use 'roundf' instead of 'ceilf'