Add some more docstrings for SBCompileUnit and SBBreakpoint, plus incorporate...

Add some more docstrings for SBCompileUnit and SBBreakpoint, plus incorporate the doxgen doc block of

SBValue::GetChildAtIndex(uint32_t idx, 
                         lldb::DynamicValueType use_dynamic,
                         bool can_create_synthetic);

into the SBValue docstrings.

llvm-svn: 135295