GENERAL DESCRIPTION
The purpose is to offer config files functionality with calculations that can be specified

IN SCOPE
- parsing config files in toml
- simple merging config files, with files order specified
- in config calculation (after merging) using calculation strings
- calculations performed on numbers (float or Decimal)
- using math functions in calculation strings (math module)

OUT OF SCOPE (for now)
- using custom functions in config calculation strings
- other syntaxes than toml
- non files config sources (e.g. CLI)
- writing config files
- calculations on arrays
- config testing on limited scope

REQUIREMENTS
- read config files in toml
- configs into a dict like structure in python
- decimal numbers can be read as floats or Decimal (config setting)
- merge config files in specified order
- perform calculations specified by calculation strings, after merging