1) add a function to get specified number of the first lines
hra_core.io_utils.get_first_lines(_file, count=1)

2) add new 2 statistics classes (Porta index):
hra_math.statistics.statistics.NdStatistic
  to get number of decelerations

hra_math.statistics.statistics.NaStatistic
  to get number of accelerations

3) add new poincare plot parameter named 
-dynamic_2_plots_headers (--dynamic_2_plots_headers)
identifiers of headers (included in output files), used to draw two
plots of parameters in one picture,
one could include many pairs of parameters, all separated by comma

a new function is added used to create two variables plots:
hra_math.utils.plot_utils.create_2_plots(_source_file, headers,
separator, window_size=None)
    draw to plots base on data from _source_file and collection of
headers
    identifiers separated by comma and grouped by 2