Add :init to ratio

[Affonso-Gui]

Current:

eus$ (instance ratio :init)
;; eus 0 error: cannot find method :init in (send #:inst60 :init)
eus$ (instantiate ratio)
;; eus 0 error: number expected in euserror

Proposed:

eus$ (instance ratio :init 1 2)
1/2

Not sure if all the makefile changes are necessary (although seem to be sufficient).

[k-okada]

@Affonso-Gui why you removed prin1 ?, please also update doc/test

[Affonso-Gui]

Removed prin1 because

1. printratio is already doing the job https://github.com/euslisp/EusLisp/blob/master/lisp/c/printer.c#L219-L226
2. extnum.l and its :prin1 method are currently not being loaded in euslisp.

[Affonso-Gui]

@k-okada Added test code. There seems to be no ratio-related documentation to be updated. We can add some if that is the case, preferentially in #359 (am planning on working on that PR this week)

[Affonso-Gui]

Tests fail/pass as expected

[Affonso-Gui]

@k-okada Please review

[k-okada]

@Affonso-Gui do we have a document for this?

[Affonso-Gui]

@k-okada Currently we have no documentation for ratio in jmanual. Should I add some (including the :init method from this PR)?

[k-okada]

Should I add some (including the :init method from this PR)?

yes please

[Affonso-Gui]

@k-okada Created at #381