* limit range of environment variable for loading the native library in Java to "true".
This change specifies the range of values that are allowed to set the environment
variable "z3.skipLibraryLoad".
Only the value "true" (in upper-, lower-, and mixed-case is accepted as valid value.
Other values, such as "false", "0", "1", "foo", an empty or a missing value are
evaluated to "false" and cause the default loading of the native library.
* adding documentation about environment variable for (not) loading the native library in Java.
This is a follow-up commit for #4667 to provide a publicly visible documentation.
