List of naming and other issues

[DavidSagan]

• Change Lat struct name to Lattice? And should all function names be consistent?
• Change Ele struct name to Element? And should all function names be consistent?
• Change use of β and γ characters for variable and function names to beta and gamma?
• Change Kn1, Kn2, etc to K1, K2, etc?
• For LCavity elements: use voltage_err or dvoltage as the voltage difference between actual and reference?
• For holly_types, should values be upper case even though they are structs?
• For a bend: Should bend_field be used as the name of the design bend field?
• Only instantiate lord branches as needed?
• Combine ThickMultipole and Multipole into Multipole which can have finite length?
• Combine Collimator and Mask into single element?
• Should CLOSED geometry be replaced by PERIODIC as being more descriptive
• Should stuff in core.jl be put in SimUtils.jl?
• Move ParticleState to SimUtils (along with enum functions)?
• Should SimUtils.jl be renamed AcceleratorUtils.jl?
• Should fint and hgap be eliminated? Should fint1 and fint2 be a vector? Should fint and hgap be combined into one parameter (edge_int)?
• UnionEle, or Container, or ContainerEle?
• Should positive dvoltage_ref mean accelerating for the reference particle?
• Change name machine coordinate system to branch coordinate system?
• Change name QuaternionX, Y, Z to x_rot (rot_x?), etc.?
• Drop Group suffix for element parameter group structs?
• Disable Ele.Group syntax(?) to make bypassing lattice bookkeeping harder.
• Add output parameters to FloorPositionGroup: _tot (with alignment), rot angles.
• Add arguments to eles function to sort_sort_by_s (default true) and include superpass and multipass lords.
• Rename Group suffix to Param

[mattsignorelli]

I added another point