Fix package-lint warnings

Reported by https://melpa.org/#/package-lint

islisp-mode.el

1:0: warning: The package summary should not end with a period.

islisp-hyperdraft.el

1:0: warning: The package summary should start with an uppercase letter or a digit.
178:0: error: "islisp-lookup-documentation" doesn't start with package's prefix "islisp-hyperdraft".

inferior-islisp.el

1:0: error: package.el cannot parse this buffer: Search failed: ";;; inferior-islisp-.el ends here"
69:0: error: "islisp-prev-l/c-dir/file" doesn't start with package's prefix "inferior-islisp".
69:0: error: `islisp-prev-l/c-dir/file' contains a non-standard separator `/', use hyphens instead (see Elisp Coding Conventions).
79:0: error: "islisp-eval-region" doesn't start with package's prefix "inferior-islisp".
85:0: error: "islisp-eval-string" doesn't start with package's prefix "inferior-islisp".
89:0: error: "islisp-do-defun" doesn't start with package's prefix "inferior-islisp".
98:0: error: "islisp-eval-defun" doesn't start with package's prefix "inferior-islisp".
103:0: error: "islisp-eval-last-sexp" doesn't start with package's prefix "inferior-islisp".
122:0: error: "islisp-load-file" doesn't start with package's prefix "inferior-islisp".
135:0: error: "islisp-compile-file" doesn't start with package's prefix "inferior-islisp".