#324 LineScan.fitSpline implemented

Implemented <b>LineScan.fitSpline</b> based on <code>http://www.scipy.org/Cookbook/Interpolation</code><br>
This is my first pull request so please bear with me if there are any errors.<br>
Looking forward to some feedback.
A an example of the function in action:

<code>import matplotlib.pyplot as plt</code>
<code>img = Image('lenna')</code>
<code>ls = img.getLineScan(pt1=(50,50),pt2=(75,75)).normalize()</code>
<code>spline1 = ls.fitSpline(degree=1)</code>
<code>spline2 = ls.fitSpline(degree=2)</code>
<code>plt.plot(ls)</code>
<code>plt.show()</code>

![ls](https://f.cloud.github.com/assets/1679435/377255/1fe1ad34-a48f-11e2-9133-abf2bb352fb6.png)
<code>plt.plot(spline1)</code>
<code>plt.show()</code>

![spline1](https://f.cloud.github.com/assets/1679435/377258/2ca15042-a48f-11e2-881a-197f7c67e887.png)
<code>plt.plot(spline2)</code>
<code>plt.show()</code>
![spline2](https://f.cloud.github.com/assets/1679435/377259/37e82dcc-a48f-11e2-94c9-a57f28909fa4.png)