config: rename addresses

WARNING: change breaks old configs.
@whyrusleeping @perfmode

This commit changes the way addresses are stored in config files.
It lumps Identity.Address and RPCAddress into Addresses. This
commit also fixes several golint issues.
config: changed language from Peers to Bootstrap
Merge pull request #121 from jbenet/feat/addrs-in-config

config: rename addresses
Implement ipfs init -d (change datastore location)
Refactor config file location, add IPFS_CONFIG_DIR

Removed config.Filename and replace it with config.GetConfigFilePath that
takes a configuration directory as argument instead. Makes code simpler.
ipfs.getConfigDir now also return the default configuration dir instead of
an empty string in some cases.
Correct style.
Fix error handling
Check the datastore is writeable when initializing