Streaming parser for STEP file

[termoshtt]

Sometimes STEP file is too large (>1GB) to expand it on memory. Since it is ASCII file, the size of files almost x10 larger than what we actually need. See ARCHITECTURE.md for detail.

[g-rauhoeft]

This is actually one of the points of criticism of the STEP format mentioned on Wikipedia: https://en.wikipedia.org/wiki/ISO_10303-21

It stores forward and backwards references in the file, which makes it difficult to handle if the whole structure isn't in memory and also hinders sequential parsing.

I'm guessing some workaround could be found with placeholder references or something of the likes.