Simplify Rayleigh-Ritz.jl

[ohno]

This issue is related to #3.

• Add struct RayleighRitzMethod in the same way as FDM.
• Separate the following functions from solve:
  • verification,
  • calculating expectation values.
• Add a new struct for the results of optimization.
• Separate the string for solve and optimize.
• Remove the optional variable info.