v0.2.4

NamedTrajectories v0.2.4

Diff since v0.2.3

Merge trajectories

• Merge function joins trajectories
• Free time and fixed time conversion moved here from QuantumCollocation

Merged pull requests:

• Fix ylims to use each key separately (#53) (@andgoldschmidt)
• Feature/merge trajectories (#54) (@andgoldschmidt)