v0.1.0

Release notes:

• Added Backbone{N} type for storing coordinates of atoms in a backbone with N atoms per residue.
  • Added constructors for creating a backbone from residue locations and rotation matrices or quaternions
  • Added locs_and_rots function for converting backbone to locations of residues and their rotation_matrices.
  • Added add_oxygens function for estimating the oxygen positions in a backbone, based on the N, CA, and C positions.
• Added Chain type for wrapping a backbone with additional information such as chain name and secondary structure.
• Added Protein type for wrapping a vector of chains and allowing for accessing chains by name instead of just index in vector.
• Added SecondaryStructure type with singleton instances Loop, Helix, and Strand for filling secondary structure vectors of chains.
• Added assign_secondary_structure! function for assigning secondary structure to the chains of a protein.
• Added IO functions for reading PDB files and loading them into proteins, and vice versa.
• Added atom_coord_matrix function for getting all coordinates of a certain atom in a backbone.