Sequel: add modulus support

extract_year.rb

ds_1 = People.select(:birth).select_append{year(:birth).as(:year)}
ds_1.first ##<Member @values={:birth=>1980-09-15 00:00:00 -0700, :year=>1980}>

ds_2 = People.select(:birth).select_append{(year(:birth) % 100 ).as(:year)}

# ds_2.first
# NoMethodError: undefined method `%' for #<Sequel::SQL::Function @name=>:year, @opts=>{}, @args=>[:birth]>

# Mostly because it is less common.  It's defined in BitwiseMethods, which is only included in NumericExpression by default.
# Some of the BitwiseMethods overlap with the BooleanMethods that are included in GenericExpression.
# Not all databases support modulus for all numeric types.  For example, SQLite doesn't appear to support modulus
# for floating point numbers, always returing NULL.  The reason it's defined in BitwiseMethods is it is mostly useful
# for integers (just like the bitwise operators), not for other numeric types.
# If you want, you can define the % method in NumericMethods if you want it to be available for most expression objects:
#  Sequel::SQL::NumericMethods.send(:define_method, :%, Sequel::SQL::BitwiseMethods.instance_method(:%))
# Note that % is already defined for Sequel::LiteralString, which includes NumericMethods but not BitwiseMethods,
# so defining % in NumericExpression can affect backwards compatibility.

Sequel::SQL::NumericMethods.send(:define_method, :%, Sequel::SQL::BitwiseMethods.instance_method(:%))

ds_2.first
# <Member @values={:birth=>1980-09-15 00:00:00 -0700, :year=>80}>