Output sanitisation (#1942)

* Add output sanitization defaults to context.send
Add some common regex filters in redbot.core.utils.common_filters
Add a wrapper for ease of use in bot.send_filtered
Sanitize ModLog Case's user field (other's considered trusted as moderator input)
Sanitize Usernames/Nicks in userinfo command.
Santize Usernames in closing of tunnels.

* Add documentation

redbot/core/bot.py

@@ -22,6 +22,7 @@ from . import Config, i18n, commands
 from .rpc import RPCMixin
 from .help_formatter import Help, help as help_
 from .sentry import SentryManager
+from .utils import common_filters
 
 
 def _is_submodule(parent, child):
@@ -292,6 +293,39 @@ class RedBase(BotBase, RPCMixin):
             if pkg_name.startswith("redbot.cogs."):
                 del sys.modules["redbot.cogs"].__dict__[name]
 
+    async def send_filtered(
+        destination: discord.abc.Messageable,
+        filter_mass_mentions=True,
+        filter_invite_links=True,
+        filter_all_links=False,
+        **kwargs,
+    ):
+        """
+        This is a convienience wrapper around
+
+        discord.abc.Messageable.send
+
+        It takes the destination you'd like to send to, which filters to apply
+        (defaults on mass mentions, and invite links) and any other parameters
+        normally accepted by destination.send
+
+        This should realistically only be used for responding using user provided
+        input. (unfortunately, including usernames)
+        Manually crafted messages which dont take any user input have no need of this
+        """
+
+        content = kwargs.pop("content", None)
+
+        if content:
+            if filter_mass_mentions:
+                content = common_filters.filter_mass_mentions(content)
+            if filter_invite_links:
+                content = common_filters.filter_invites(content)
+            if filter_all_links:
+                content = common_filters.filter_urls(content)
+
+        await destination.send(content=content, **kwargs)
+
     def add_cog(self, cog):
         for attr in dir(cog):
             _attr = getattr(cog, attr)