Make read (rdrecord, rdsamp) and write (wrsamp) functions isomorphic

[briangow]

As noted in #484 , rdsamp and wrsamp are not isomorphic. It is reasonable to expect that what gets read into memory should be sufficient and by default re-create the read file when passing that information to a write function.

We should provide a set of isomorphic read and write functions by doing at least one of these:

1. Making rdsamp and wrsamp isomorphic. Currently they only handle a subset of the parameters in a record object though.
2. Adding a write function which can use all of the information from rdrecord to re-create a read record.