organize imports
privatize getLedger method
substitute with LedgerMap type
hide ledger wantlist manipulation
privatize fields in ledger
fix(bitswap:ledger) race conditions

https://github.com/jbenet/go-ipfs/issues/39
Merge pull request #38 from jbenet/feat/bitswap-import-cleanup

chore(bitswap) tidy up bitswap, ledger
config: Broke out config directory into its own const
config: Made WriteConfigFile create config parent directory if it doesn't exist
cmd/init: Fixed init checking if config exists
Merge pull request #49 from mappum/feat/init-fix

Init Fix
core: Refactored node initialization
core: Don't require address for node initialization
core: Show error when config identity is not set
core: Updated basic initialization tests
Merge branch 'master' of github.com:jbenet/go-ipfs into ipns

Conflicts:
	core/core.go