provide data helper functions

[juniperlsimonis]

the input to LDA_TS is in a format that may not be familiar to many folks, especially in ecology, so it will help lower barriers for users if we create some basic functions to convert possible data option types that users might have into what LDA_TS needs. such functions might also be able to be integrated into LDA_TS itself through the conform_LDA_TS_data function that happens internally

[juniperlsimonis]

ref: #119

[juniperlsimonis]

also, conversion back to user-input times will be nice, ref #123

[juniperlsimonis]

a specifically important instance of this general issue is the non-integer times, as discussed in #126