Fix byte-compilation error

[occidens]

@shanecelis, are you still maintaining this package?

I was trying to re-install this from MELPA (the recipe was submitted by @yasuyk), but it throws a byte compilation error:

hideshow-org.el:112:1:Error: Symbol's value as variable is void: hs-org/trigger-keys-block

hideshow-org.el loads fine; it just can't be byte-compiled from a "cold" start because defvar does not bind variables at compile time, and the variables hs-org/trigger-keys-block and hs-org/trigger-keys-all are required for the expansion of the macro hs-org/define-keys.

This PR is one way of fixing the issue: the keymap for the minor mode is defined at load time, rather than compile time. I've tested this on my machine and it byte compiles without error.