System environment and resource management

This is a package that handled the system environment variables and especially the search path for Singular resources (like libraries and modules).

This may be used by factory in order to search for its precomputed tables and thus have been separated into a standalone top-level package.

Note that this package has no further dependencies, while it is used by the rest of Singular packages:

• Multivariate polynomial factorization (factory),
• Basic Data Structures,
• Several involved mathematical algorithms (kernel),
• Singular Interpreter and related functionality.