Declare php ext dependencies (bcmath and mbstring) in composer.json

Signed-off-by: Rogerio Prado de Jesus <rogeriopradoj@gmail.com>
Change the "require" for "suggest" extensions

Signed-off-by: Rogerio Prado de Jesus <rogeriopradoj@gmail.com>
Merge pull request #128 from rogeriopradoj/declare-php-ext-suggestions

Declare php ext suggestions, fix #121 PR#128 @rogeriopradoj