Fixed issue [#1162](https://github.com/jgm/pandoc/issues/1162).

Modified Text/Pandoc/Readers/HTML.hs
- Edited pInlinesInTags to use a newly defined function splitSpaces

Modified Text/Pandoc/Shared.hs
- Added a new exposed function splitSpaces which is a more general
  version of normaliseLines. splitSpaces returns a 3-tuple.
  P1: A space if there are any leading spaces
  P2: The normalised body of the text
  P3: A space if there are any trailing spaces
  normaliseLines is then implemented in terms of splitSpaces.

It should be investigated if this bug is only local to pInlinesInTags
or to any function which utilised normaliseLines.
Merge branch 'master' of https://github.com/jgm/pandoc