Allow pad value to be passed as an option for compute()

First off, thanks for doing the hard work of porting this algorithm to JS! :)

In an app of mine I'm passing a rectangular matrix to compute(). However, since compute() doesn't pass in a pad_value for pad_matrix() the matrix will get padded with zeroes. Thus, I order to pad the matrix with some other value I currently need to call pad_matrix() separately before compute(). It would be sweet if one could pass in the pad_value as an option for compute() removing the need for an extra call to pad_matrix().

The other two commits are for stripping the whitespace in munkres.js and refactoring some of the documentation from Python to JSDoc format. Feel free to ignore all of this, or cherry-pick the ones worth merging.