[Feature Request] Support extended-globs, automatically expand parent directories.

[showhwa]

#1589

old:

[[backup.snapshots]]
sources = ["/"]
iglobs = [
"!*",

**"/A",**
"/A/**",

**"/B",**
**"/B/C",**
"/B/C/**",

**"/D",**
**"/D/E",**
**"/D/E/F",**
**"/D/E/F/G",**
"/D/E/F/G/**"
]

new:

[[backup.snapshots]]
sources = ["/"]
e-iglobs = [
"!*",

"@/A/**",

"@/B/C/**",

"@/D/E/F/G/**"
]

This is just a suggestion.
Of course, if there's a simple way to use globs without changing the code, please let me know.