rotations version 0.2

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Changes -

* Multiple columns can be supplied to `col` in `plot` via grid.arrange.  Each requested column is identified by its axis and one legend is printed when applicable.  For example `col=c(1,3)` will print two labelled eyeballs, one for the x- and one for the z-axis.

* Quaternions are only unique up to their sign, that is if q is a quaternion the q=-q.  So `==` has be redefined such that `q==-q` will return `TRUE`.

* In 'dist' the 'method' arguement now accepts the option 'extrinsic' and returns the same result had the 'projected' option been used.

New Features -

* The `'['` operator has been redefined to maintain the `SO3` or `Q4` class of the object.

* Addition `+` and subtraction `-` have been redefined for the multiplicative group SO(3).  That is, for R1 and R2 in SO(3), R1+R2=R2R1, R1-R2=R2'R1 and -R1=R1'.  Similarly for quaternions.

* The `head` and `str` functions have been modified to properly handle objects of class `'SO3'` and `'Q4'`.

* Functions for Bayesian analysis
  * Each of the following functions requires the user to supply `type`, `tuneS`, `tuneK`, `burnin` and `B`.  These arguments  determine the transition probability form, tuning parameters for the central orientation, concentration parameter, burnin for the MCMC and total number of draws from the posterior, respectively.  Currently only `'Cayley'`, `'Fisher'` and `'Mises'` are valid options for `type`.  See the respective help files for more details.
  * The function `MCMCSO3` implements a Gibbs-within-MCMC algorithm to get draws from the posterior distributions for the concentration parameter $S$ and concentration parameter $\kappa$.  A list of four items is returned: `S` is a B-by-p matrix where each row corresponds to a draw from the posterior for the central orientation S, `kappa` is a vector of B draws from the posterior for the concentration parameter $\kappa$ and the transition probabilities for the central orientation and concentration are given by `Saccept` and `Kaccept`,respectively.
  * Bayesian point estimates for the central orientation and concentration parameter are given by `bayes.mean`.
  * Bayesian credible regions have been added to the `region` by setting `method='Bayes'`. 

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rotations version 0.1

* First CRAN release