Don't define global method "assert"

[TSMMark]

pdfcrowd-ruby/lib/pdfcrowd.rb

Lines 403 to 405 in f11d34a

	def assert
	raise "Assertion failed !" unless yield
	end

conflicts with testing libraries like minitest, cutest, etc.

Should be just as easy to def assert on a pdfcrowd module instead.

Example of what can go wrong

ArgumentError: wrong number of arguments (given 2, expected 0)
    /usr/local/bundle/ruby/3.0.0/gems/pdfcrowd-4.4.2/lib/pdfcrowd.rb:403:in `assert'
    /usr/local/bundle/ruby/3.0.0/gems/cutest-1.2.3/lib/cutest.rb:159:in `assert_equal'

[foxmadr]

The method was renamed to avoid conflict.