Findpeaks

* Added xlim, ylim, zlim parameter for `plot_mesh` functionality.

Update requirements

* added function to import image from URL location: `fp.imread(path)`
* Update docststrings

* Fix in plot when using whitelist for valleys or peaks
* Added xlabel and ylabel to plot

fp.plot(xlabel='x-axis', ylabel='yaxis')
fp.plot_persistence(xlabel='x-axis', ylabel='yaxis')

* various fixes for plotting the persistence, and adding fontsize


Import library
from findpeaks import findpeaks
Initialize
fp = findpeaks(method='topology')
Example 1d-vector
X = fp.import_example('1dpeaks')

Fit topology method on the 1d-vector
results = fp.fit(X)
Plot the results
fp.plot_persistence(fontsize_ax1=12, fontsize_ax2=14)
Remove labels for ax1
fp.plot_persistence(fontsize_ax1=None, fontsize_ax2=14)

* Fix for plot_persistence() that not always showed up