Removing the -a option.

Appending output to a configuration file can very easily be done with
simple terminal commands and this tool does not need to offer that.
Removing the last newline of -c.
Removing an unused dependency.
Fixing a bug with rates of more than one decimal.
Merging all files in ./bin.
options variable is no longer global.

This patch can more easily be visualized by using the --color-words
option of git show and git diff.

  $ git show --color-words=. HEAD
Refactoring verbose output to a method.
Error messages are now printed to stderr.
Error messages now cause an exit code of !0.
Turning the library into a gem.
Adding installation instructions to the README.
The version constant now resides in version.rb.
Removing unnecessary code (runs fine without it).
The --dry option now implies --verbose.
Some refactoring and variable name changing.
Config file is no longer created automatically.

This was completely unnecessary and only a weird side effect of
requiring the library.
One can now specify a path to the config file.
Removing PKGBUILD from this repository.

The PKGBUILD may now be found in a dedicated repository [1] for all the
packages that I maintain.

[1] https://github.com/badeball/archpackages
Adding a command line option to show version.
Adding a changelog to the README.