fix: Move ext-intl and ext-bcmath out of require and into suggest blo…

[pointybeard]

…ck (closes #187)

Relates to #187

There is existing code to check that ext-intl and ext-bcmath are installed. Including them in the require block of composer.json is too restrictive and does no allow this package to be used on systems without them even though ext-intl is only used for spellout() and SimpleCalculator can be used instead of BinaryCalculator.

This change moves them into the composer suggest block instead, allowing the code to throw exceptions where necessary.