implement set cache directory

Hi,
find below a patch which let user set a custom chache folder.

Environment variable OFFPUNK_CACHE_PATH is used.
This way, it can be set globally in a profile, or occasionnaly before running offpunk.
It also avoid the pain to parse options and dealing with flags in scripts.
Thank you for your attention.

Regards.

prx

man/netcache.1

@@ -27,6 +27,15 @@ otherwise it would always refresh it from the version available online.
 It is also useful for mapping a given URL to its location in the cache,
 independently of whether it has been downloaded first.
 .Pp
+Default cache path is
+.Pa ~/.cache/offpunk .
+Set
+.Ev OFFPUNK_CACHE_PATH
+environment variable to use another location.
+.Bd -literal
+OFFPUNK_CACHE_PATH=/home/ploum/custom-cache netcache.py gemini://some.url
+.Ed
+.Pp
 .Xr Offpunk 1
 is a command-line browser and feed reader dedicated to browsing the Web,
 Gemini, Gopher and Spartan.

offutils.py

@@ -62,9 +62,12 @@ def xdg(folder="cache"):
     #if no XDG .local/share and not XDG .config, we use the old config
     if not os.path.exists(data_home) and os.path.exists(_old_config):
         _DATA_DIR = _CONFIG_DIR
+    ## get _CACHE_PATH from OFFPUNK_CACHE_PATH environment variable
+    #  if OFFPUNK_CACHE_PATH empty, set default to ~/.cache/offpunk
     cache_home = os.environ.get('XDG_CACHE_HOME') or\
                     os.path.join(_home,'.cache')
-    _CACHE_PATH = os.path.join(os.path.expanduser(cache_home),"offpunk/")
+    _CACHE_PATH = os.environ.get('OFFPUNK_CACHE_PATH', \
+        os.path.join(os.path.expanduser(cache_home),"offpunk/"))
     os.makedirs(_CACHE_PATH,exist_ok=True)
     if folder == "cache" and not UPGRADED:
         upgrade_cache(_CACHE_PATH)