add blank line in a dosctring
implement a generic prior class
parameter class defined in data, prior instance introduced
Starting point of Nested Sampling implementation

added a new flag in the parser, -m, that expects a string. By default,
it is 'MH' for Metropolis Hastings, but can be set to 'NS'.

Then, a file called sampler.py was added, which is not called from
MontePython instead of mcmc. The discrimination between mcmc and
nested sampling will be inside of this new sampler module's function
called `run`. The implementation of the nested sampling will be done
in a separate branch, branching off here
Code refactorize from mcmc to sampler, for generic methods

four different methods were transfered from the mcmc module to the
sampler module, because they were more general. These are
`get_covariance_matrix`, `read_args_from_chain` and `_bestfit`, and
`accept_step`.

The documentation has been also altered to reflect these changes, as
well as previous modifications. It now also tells in the installation
page that installing WMAP likelihood is not necessary.
Add a VERSION file, and a scheme to read it in the code
documentation read version number automatically
Changes to prior.py specific for nested sampling
Minimal implementation, apparently working
Oops\! Last commit reverted: it should only go to the nested_sampling branch
Improved example_ns.param. Almost empty commit to set the branch going.
simpler version of test example ns
Minimal working example + plotting script
do not create chains when running Nested Sampling
fix documentation in io
basic interfacing with chains
good version of NS, example with fake planck
pushed version number in README
refactorise NS implementation
improved pylint