Runs and fix typos

It has been a long time that I have created this notebook. I have rerun
it in order to check if it is OK. It is. I also fixed some typos.
Write test functions to synfit function

There were some codes that I sued to test the synfit function. I have
wrapped it in test functions.
Write test functions for the others functions

I wrote test functions for tow more functions: `break_args` and `iterator`.
Improves docstring of `iterator` function.
Adds support to windows

The user can now set a range of wavelength in which `synfit` will work on.
Change function to accept more than 1 element

The `break_args` function now accepts more than one chemical element.
This is crucial to study blended spectral lines.
Adds support for radial velocity and fix windows
Makes `synfit` into an object

I have changed the `synfit` function into an object.

All functions have been adapted to this, including the functions that
test the fits.
Removes `iterator` from `Synfit`

I removed the `iterator` function from the `Synfit` class because I need
it in two separate parts of the class. And also because it seems to be a
general purpose function that I could use somewhere else.
Creates a fitting package

This package contains a routine to automatically fit the spectral lines.
The routine was strongly influenced by Ivan Hubeny's `synfit`. In short,
it synthesize spectra in a set of values and compare with the
observation by calculating the chi-square. The minimum chi-square will
give the best values.

There is still room to improve, like applying a convergence method.
Adds test suite for Synfit

I used `nosetest` to run it and all of them passed.
Adds test functions to complementary function

These functions tests two complementary functions of Synfit.
Remove unnecessary text and code

I have already transfered it to S4 and it is now operational, thus there
was no need of the code and text anymore.
Initialize empty parameters inside __init__

It was initializing some parameters outside __init__. It seems that this
is not a good programming practice.
Adds function to plot best fit

The Synfit object has now a module to plot the best fit.
Check if the input parameters are correct

It checks if the input parameters are correct. If not, throws an error
with an explanation.
Removes check for radial velocity

In the __init__, it already sets the value of radial velocity, so there
is no need to check it.
Improves plot

The plot of each iteration now shows the value of the calculated
chisquare. I had to do an workaround so the synthetic and the observed
spectra would match in scale and radial velocity.
Merge branch 'development' into feature-fitting
Clarify length of windows

I found that the window can only be a single block, i.e., I cannot have
multiple windows.

I added a description about this on the documentation and make it sure
in the code.

It is desirable to have multiple windows, then one can measure, for
example, just the wings of the spectral line.