Template plist to work around launchd limitations

`launchd` doesn't allow you to *use* environment variables. Nor does it support
tilde-expansion of program names & arguments after OSX 10.10.

To work around this, I've made the plist file a template and included a small
install script that will interpolate the correct values.

misc/launchd/README.md

 # ipfs launchd agent
 
-A bare-bones launchd agent file for ipfs. To have launchd automatically run the ipfs daemon for you, do the following:
-
-    mkdir -p ~/Library/LaunchAgents
-    cp misc/launchctl/io.ipfs.ipfs-daemon.plist ~/Library/LaunchAgents/
-    launchctl load ~/Library/LaunchAgents/io.ipfs.ipfs-daemon.plist
+A bare-bones launchd agent file for ipfs. To have launchd automatically run the ipfs daemon for you, run `./misc/launchd/install.sh`
 
 Note that the `ipfs` binary must be on the *system* PATH for this to work. Adding a symlink in /usr/bin works well enough for me.

misc/launchd/install.sh

+#!/bin/bash
+
+src_dir=$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )
+plist=io.ipfs.ipfs-daemon.plist
+dest_dir="$HOME/Library/LaunchAgents"
+IPFS_PATH="${IPFS_PATH:-$HOME/.ipfs}"
+escaped_ipfs_path=$(echo $IPFS_PATH|sed 's/\//\\\//g')
+
+mkdir -p "$dest_dir"
+
+sed 's/{{IPFS_PATH}}/'"$escaped_ipfs_path"'/g' \
+  "$src_dir/$plist" \
+  > "$dest_dir/$plist"
+
+launchctl list | grep ipfs-daemon >/dev/null
+if [ $? ]; then
+  echo Unloading existing ipfs-daemon
+  launchctl unload "$dest_dir/$plist"
+fi
+
+echo Loading ipfs-daemon
+launchctl load "$dest_dir/$plist"
+launchctl list | grep ipfs-daemon

misc/launchd/io.ipfs.ipfs-daemon.plist

@@ -11,12 +11,17 @@
       <string>ipfs</string>
       <string>daemon</string>
     </array>
+    <key>EnvironmentVariables</key>
+    <dict>
+      <key>IPFS_PATH</key>
+      <string>{{IPFS_PATH}}</string>
+    </dict>
     <key>RunAtLoad</key>
     <true/>
     <key>StandardErrorPath</key>
-    <string>/usr/local/var/log/ipfs.err</string>
+    <string>{{IPFS_PATH}}/logs/stderr.log</string>
     <key>StandardOutPath</key>
-    <string>/usr/local/var/log/ipfs.log</string>
+    <string>{{IPFS_PATH}}/logs/stdout.log</string>
   </dict>
 </plist>