Remove support for reading packaged.srg

packaged.srg is created by FML/MCP from joined.srg
and packages.csv. Now that we support reading packages.csv,
remove support for packaged.srg; one fewer codepath.
Add support for remote --in-jar URLs

You can now provide an HTTP URL to --in-jar and
it will be downloaded to a temporary file before
remapping. Example:

java -jar target/SpecialSource-1.3-SNAPSHOT-shaded.jar --in-jar http://assets.minecraft.net/1_4_7/minecraft_server.jar --out-jar /tmp/net.jar --srg-in ../MinecraftForge/mcp/conf/
Update date to 2012-2013
Add support for remote --srg-in mappings

Mappings can now be downloaded from remote URLs. Both
individual .srgs and directories of .srg/.csv are supported.
Examples:

java -jar target/SpecialSource-1.3-SNAPSHOT-shaded.jar --in-jar http://assets.minecraft.net/1_4_7/minecraft_server.jar --out-jar /tmp/net.jar --srg-in https://raw.github.com/MinecraftForge/FML/master/conf/joined.srg
java -jar target/SpecialSource-1.3-SNAPSHOT-shaded.jar --in-jar http://assets.minecraft.net/1_4_7/minecraft_server.jar --out-jar /tmp/net2.jar --srg-in https://raw.github.com/MinecraftForge/FML/master/conf/