added read support for step files, along with its tests. write support is a little bit more complicated, we'll work on it
added write support (with tests) for step files
added namespace and () to the read_STEP and write_STEP name functions in the doc/changes.h file; removed some extra empty line from the function implementation in utilities.cc
Merge pull request #245 from andreamola/added-STEP-support

Added step support