Release v0.8.3

What's Changed

• Tomiya-san by @terasakisatoshi in #87
• Allow ScalarPhi4Action to specify various precisions e.g. Float64 by @terasakisatoshi in #88
• Adam to adam by @terasakisatoshi in #89
• remove main.jl and write the content in docstring of train function by @terasakisatoshi in #91
• Del unused packages by @terasakisatoshi in #90
• add HMC code by @terasakisatoshi in #92
• prepare release 0.8.3 by @terasakisatoshi in #93

Full Changelog: v0.8.2...v0.8.3