Allows random seeds

- Added an optional input argument ‘rndseed’ to majjags.m
- If it is set equal to 1, then a random seed will be generated with
every call to the mat jags function. Each chain is initiated with this
random seed + the chain value.
- Added an example use of the flag in Example1.m
updated info about use of new 'rndseed' flag
Merge pull request #2 from drbenvincent/master

Added ability to randomise the seed of each chain