Copyright (C) 2015 Jeffrey M Brown

This program is free software: you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation, either version 3 of the License, or (at your
option) any later version.

This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
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General Public License for more details.

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The Parameters class provides a simple way to manage input files
commonly used in simulations. Parameter files contain key=value pairs
that can be grouped under sections, denoted by square braces:
[section]. Comments are also allowed. Any text after a hash symbol #
is ignored. An example input file would contain:

# this is a comment
[time]
N = 1024  # another comment
dt = 0.1

[space]
N = 256
dx = 1e-6

[output]
filename = mydata.dat


These pairs will be stored in a map with each section name prepended
to the keys. The above input file would be stored in a std::map as:

time/N   : 1024
time/dt  : 0.1
space/N  : 256
space/dx : 1e-6
output/filename : mydata.dat


To read an input file, create a parameters object:

  Parameters::Parameters params(filename);


To use a value associated with a particular key, first create a
variable in your program and then call the get member function:

  double dt;                // dt = 0.0
  params.get("time/dt", dt) // dt = 0.1


Parameters uses templates and stringstreams in order to decipher the
type. You can also get a Parameters object of a particular section
using:

  Parameters::Parameters p = params.getSection("space")