Implement process investment constraints #1069
Description
Since #1020 we have an input file for investment constraints, allowing users to specify the maximum investment in a particular process in a given year/region. However, this constraint still needs to be implemented.
See #124 for some important points about this, in particular:
- Adam's advice that limits should be split between agents in proportion to their share of the primary commodity
- That the limit is per year, not per milestone year, so must be adjusted to account for the gap between milestone years