…year-time-scale' and 'dispatch-chain' into release
Fixes #428. This is built on top of existing tick support for linear scales: for small intervals, a linear scale computes ticks based on milliseconds; for large intervals, a linear scale computes ticks based on fractional years. This commit also extends the time scale's formatter to display milliseconds.
There's an edge condition which is not discussed in the original algorithm ("Visualization of Large Hierarchical Data by Circle Packing", Wang et. al): what happens if the first intersecting circle C_j is equidistant from C_m and C_n? In other words, it is both after C_n on the front-chain, and before C_m. The correct answer is that you should splice the smaller of the two circles. If C_m is smaller than C_n, then splice from C_j to C_n and set C_m to C_j; otherwise, splice from C_m to C_j, and set C_n to C_j.