Fix several ResourceWarnings: unclose file

[BoboTiG]

Hello,

This is a little patch for resource leaks such as:

$ python setup.py install
setup.py:14: ResourceWarning: unclosed file <_io.TextIOWrapper name='README.rst' mode='r' encoding='UTF-8'>
  long_description=open("README.rst").read(),
running install
...

$ bash examples/sample.sh
scatterplot.py:100: ResourceWarning: unclosed file <_io.TextIOWrapper name='examples/data/texas.txt' mode='r' encoding='UTF-8'>
  plot_scatter(opts.f, opts.x, opts.y, opts.size, opts.pch, opts.colour, opts.t)
with x and y coords
scatterplot.py:57: ResourceWarning: unclosed file <_io.TextIOWrapper name='examples/data/x_test.txt' mode='r' encoding='UTF-8'>
  xs = [float(str(row).strip()) for row in open(xs)]
scatterplot.py:58: ResourceWarning: unclosed file <_io.TextIOWrapper name='examples/data/y_test.txt' mode='r' encoding='UTF-8'>
  ys = [float(str(row).strip()) for row in open(ys)]

histogram.py:109: ResourceWarning: unclosed file <_io.TextIOWrapper name='examples/data/exp.txt' mode='r' encoding='UTF-8'>
  f = open(f).readlines()

I also fixed this error:

Traceback (most recent call last):
  File ".../bin/scatter", line 11, in <module>
    load_entry_point('bashplotlib==0.6.5', 'console_scripts', 'scatter')()
  File "scatterplot.py", line 100, in main
    plot_scatter(opts.f, opts.x, opts.y, opts.size, opts.pch, opts.colour, opts.t)
  File "scatterplot.py", line 74, in plot_scatter
    if cs:
UnboundLocalError: local variable 'cs' referenced before assignment

Signed-off-by: Mickaël Schoentgen contact@tiger-222.fr