Create the new variables and constraints for the use of a tighter formulation for storage assets

[datejada]

• There is a new binary variable to avoid charging and discharging simultaneously.
• Extra constraints shown in Update the documentation (formulation and tutorial/how-to) with the use of a tighter formulation for storage assets #640

[datejada]

After a discussion with @g-moralesespana:

• Binary variable resolution: lowest in/out flows to the storage asset. For example, one flow is for charging with a resolution of 1h, and the other is for discharging every 2h. The binary resolution should be every 2h.
• Using the binary method, the capacity constraints are still written in the highest resolution to guarantee that the bounds of the flows are in power.