Update examples

[spyridon97]

1. Writers to use BeginStep(), EndStep()
2. Make sure readers call BeginStep() before using AvailableVariables()/InquireVariables()
3. Convert BP3/BP4/BP5 to BPFile

[spyridon97]

@anagainaru @eisenhauer @pnorbert if you have in mind anything else to updates write it here.