Make it easier to install YottaDB from a source or binary tarball

README.md : Make it easier to build and install YottaDB from source

ydbinstall.sh a) Fix more occurrences of GT.M/gtm to YottaDB/ydb b) Make help more useful by printing some example usages c) Do not print full help in case of an error. Just point to help so actual error is highlighted. d) Add support for Linux on ARMV7L e) Fix bug (default case label should be "*" and not "default") f) Derive YottaDB release # (not GT.M version #) if ydbinstall and mumps are bundled together g) Issue error messages if wget fails