Fix public interface to make it nicer to use

Merge pull request #3 from bluelabs-eu/fix/constructor-functions

Fix/constructor functions

add NewFromFloat Rhymond#108 (Rhymond#116)

update: Fix ARS decimal and thousand separators

Add XOF and MGA currencies (Rhymond#110)

This patch adds West African CFA franc (XOF) and Malagasy ariary (MGA)
currencies in order to provide them in go-money library.

See also:
- [West African CFA
  franc](https://en.wikipedia.org/wiki/West_African_CFA_franc);
- [Malagasy ariary](https://en.wikipedia.org/wiki/Malagasy_ariary);

Closes Rhymond#109

Signed-off-by: r1cm3d <[email protected]>

Rhymond#106 Split of small negative values doesn't work properly (Rhy…

…mond#107)

Get Currency by Numeric Code (Rhymond#104)

* find currency by code

* get currency by code

fix negative split remainder (Rhymond#94)

Co-authored-by: Raymond <[email protected]>

Export an error for currency mismatches (Rhymond#91)

Co-authored-by: Raymond <[email protected]>

Merge pull request Rhymond#70 from nvjkmr/master

Added ISO 4217 numeric codes for currency