Line Number for Branch Points

While working with OpenCover and ReportGenerator, I realized that incomplete branch coverage is not reported, despite it's indicated in the xml file. This issue drills down to not being able to decide which source line a branching instruction corresponds to.

It turns out this information can be extracted from PDB files:
* each source instruction creates a SequencePoint in the PDB,
* we already know which offset a branch corresponds to,
* we have to find the previous SequencePoint for each branching instructions, to be able to determine which source line resulted in it.

The key idea of this change is this interval seach between SequencePoints.

Please let me know your thoughts.