feat: implement type to record internal solution

[CodeBear801]

Issue

issue: #143
solutionformat implements internal data format for charge solutions, it isolate internal algorithm with external restful api. A function of dump2RestResult will be added to solution later.

Tasklist

• code
• review

[wangyoucao577]

I feel solution will be better, even it causes solution.Solution. How's your idea?

[CodeBear801]

I like shorter name.

My original thinking is, solution is better contains not only type definition but also solution logic, which is how those type is constructed, such as the calculation logic.

Currently, I put constructing logic inside stationgraph, in the end of its calculation it will generate result in solutionformat, which could be dumped to external format. That's what I try to limit scope with solutionformat or solutiontype

But as a reviewer, I think solution is more clear than solutionformat or solutiontype.

[CodeBear801]

The following comment I think is worth to record: Avoid to use package name as variable name, otherwise you will get strange errors.

After I rename package name from solutionformat to solution, there are some existing code use this package create a variable solution there. (this code is not in this pull, they exists in the pull request #203)

solution := &solution.Solution{}
solution.ChargeStations = make([]*solution.ChargeStation, 0)

I met following error:

I think compiler confuse on whether solution is a package name or a variable name. After I rename variable solution to sol, problem solved. But it took me a while to figure it out. I original thought it is related with package renaming.