Ability to get latex without getting function name

[MAKMED1337]

import latexify
def solve(a):
	return 5 * a
print(latexify.get_latex(solve, no_function=True))

to be 5a, not \mathrm{solve}(a) \triangleq 5a

i think it's better to create another function not parameter or set by default

[odashi]

(EDIT: as for the new function names) Using latexify.expression or something similar would be good. I also guess that the current function names with_latex and get_latex is weird a little; possibly we can redefine it as latexify.equation (but we also need to keep the current functions for a while, for backward compatibility).