Remove functions that deal with abundance

I created a class that transform the abundance from a dictionary format
to the Synplot format. Now, this transformation is done by the Synplot
object.

Thus, these functions were not more necessary.
Change array of chisquare values

I started changing the code to accept the changes in the Synplot object
that address abudnance in dictionary format.

Now, I changed the chisquare_values array to be a structured array
instead of a ndarray. This will clarify what is being accesed.

Known issues:

- It has to be cleaned
- The iterator function can be merged easily into the Synfit object
- The plot_chisquare function does not work with two elements
- Abundance is not working.
Fix plot_chisquare and abundance

It now works with abundance values  and I fixed the `plot_chisquare`
function for two parameters.

Known issues:

- It has to be cleaned
- The iterator function can be merged easily into the Synfit object
- Does not work with varying and fixed abundance.
Adds support to fixed abundance

The user can now have a varying and a fixed abundance.

The downside is that both abundance should be in dictionary format.

Known issues:

- It has to be cleaned
- The iterator function can be merged easily into the Synfit object
Fix abundance

The fitting with abundance was not working. It had conflict if there was
fixed parameters.

Known issues:

- It has to be cleaned
- The iterator function can be merged easily into the Synfit object
Change the format of the input abundance.

It cannot have fixed abundances in the Synplot format. I changed it to a
dictionary.
Remove test for synplot_abund

this function was merged to the Synplot class. The test is located
elsewhere.
Join code into a method

I had two piece of code that did the same thing. I put it into a
method.
Remove iterator function

I have added it to  Synfit.
Remove test for iterator.

This function has been added to Synfit as a single line. No test is
needed (I hope).
Removes commented code

This code was commented and unnecessary.
Change name of test folder to plural
Makes a copy of abundance

It was changing the parameter outside of this object.
Merge branch 'hotfix-synplot-abund' into feature-fitting
Fix best_fit dictionary

It was only showing one parameter.
Adapt test to reflect Synfit changes

It is everything running.
Plot chisquare against abundance values

The plot of chisquare Vs. Abundance is now working.
Fix adding of fixed abundances

It was not adding it properly.
Test for fixed abundance
Create folder to store extra resources

Extra resources as files and other stuff must be put here.