Fix flycheck warnings
Promote cbm:mail-directory -> user-mail-directory in cb-paths
Redefine file-picker as a macro

* Accepts optional :default-dir argument
* Fix a few compiler errors
Add interactive command for capturing from files
Add ledger info manual
Assert elisp snippet
Fix more compiler warnings
Extract method -> filepicker--format-header
Add internal prefix for file-picker functions
Fix compiler warnings
Capture expenses from emails correctly
Redeclare buffer-undo-tree (cb-file-picker-widget.el)

Stops compiler warnings in client code.