Don't rely on move-text-default-bindings, which has been removed upstream

Fixes #168, #169
Load magit-git-wip after magit, not directly after vc
Add site-lisp dirs to load-path after creation
Also use guide-key for narrowing map via "C-x n" prefix
Allow inline completions to cycle without eagerly popping up *Completions*
Ignore helm-adaptive-history
Don't rebind C-x C-a in emacs-lisp-mode: it upsets edebug

Fixes #173
Check OS before using exec-path-from-shell for $LEDGER_FILE

See #174
Update README to clarify steps to follow before filing issues