Document compatibility aspects of getDefaultSubstitutions()

Signed-off-by: Oleg Nenashev <o.v.nenashev@gmail.com>
Add support of default core substitution variables and the computer environment

Signed-off-by: Oleg Nenashev <o.v.nenashev@gmail.com>
MacroStringHelper methods are interruptable

Signed-off-by: Oleg Nenashev <o.v.nenashev@gmail.com>