0031481: Data Exchange - provide parser of STEP EXPRESS schema for generation of...

0031481: Data Exchange - provide parser of STEP EXPRESS schema for generation of new STEP entities

Integration of ExpToCas tool ported to modern state of OCCT:
- new package Express and toolkit TKExpress for EXPRESS data structures and OCCT class generator
- executable ExpToCasExe including lax/yacc parsers, for parsing a Part 21 file and generating classes

Formatting added files from package Express following OCCT Coding Rules

Changes for correspondence generated files to OCCT Code Rules.

Add generation hxx files with declaration of arrays.
If field is a HArray1 method for get length of array and method for get element of array by its index are generated.

Changes for generation parser from Lex and YACC files.

Update description file ReadMe.md