feat: support expand env vars and home user in path_tempfile

This allows you specify paths with `~` and variables like `$HOME`:

    "path_tempfile": "~/.cache/markdownpreview"

MarkdownPreview.sublime-settings

@@ -306,6 +306,9 @@
         the OS default. The directory will be created if it doesn't exist yet.
         Relative paths are supported and are checked against `os.path.isabs`,
         see docs: http://docs.python.org/3/library/os.path.html#os.path.isabs
+        Environment variables and user "~" placeholder are supported.
+        see docs: https://docs.python.org/3/library/os.path.html#os.path.expanduser
+        see docs: https://docs.python.org/3/library/os.path.html#os.path.expandvars
 
         Examples: /tmp/custom_folder   (Linux/macOS - absolute path)
                     C:/TEMP/MYNOTES

docs/src/markdown/usage.md

@@ -129,6 +129,9 @@ via the `path_tempfile` option:
         using LiveReload and don't want to use the OS default. The directory will be created if it
         doesn't exist. Relative paths are supported, and are checked against `os.path.isabs`, see
         doc: http://docs.python.org/3/library/os.path.html#os.path.isabs
+        Environment variables and user "~" placeholder are supported.
+        see docs: https://docs.python.org/3/library/os.path.html#os.path.expanduser
+        see docs: https://docs.python.org/3/library/os.path.html#os.path.expandvars
 
         Examples: /tmp/custom_folder   (Linux/OSX - absolute path)
                     C:/TEMP/MYNOTES

markdown_preview.py

@@ -104,6 +104,7 @@ def get_temp_preview_dir(view):
     settings = sublime.load_settings('MarkdownPreview.sublime-settings')
     path_tempfile = settings.get('path_tempfile')
     if path_tempfile:
+        path_tempfile = filter_path(path_tempfile)
         if os.path.isabs(path_tempfile):  # absolute path or not
             tmp_dir = path_tempfile
         else:
@@ -114,6 +115,14 @@ def get_temp_preview_dir(view):
     return tmp_dir
 
 
+def filter_path(path):
+    """Return a path with user and variables expanded."""
+    path = os.path.expanduser(path)
+    path = os.path.expandvars(path)
+
+    return path
+
+
 def save_utf8(filename, text):
     """Save to UTF8 file."""
     with codecs.open(filename, 'w', encoding='utf-8')as f: