migratebundle: relation inference
migratebundle: factor relation filtering into its own function
migratebundle: adjust comments
Merge pull request #59 from rogpeppe/022-migrate-bundle-3

migratebundle: relation inference
charm: allow open relations in bundles
charm: minor fixes for review
fix comments for review
Merge pull request #60 from rogpeppe/023-bundle-allow-open-relations

charm: allow open relations in bundles
migratebundle: remove getCharm argument from Migrate
migratebundle: re-add getCharm argument to Migrate
Merge pull request #61 from rogpeppe/024-migratebundle-open-relations

migratebundle: remove getCharm argument from Migrate
all: use gopkg.in/errgo.v1
Merge pull request #62 from rogpeppe/024-use-errgo.v1

all: use gopkg.in/errgo.v1
charm: implement MustParseReference
Merge pull request #63 from rogpeppe/025-mustparsereference

charm: implement MustParseReference
Metrics definition parsing.

Metrics loading in charm.
Merge pull request #64 from tasdomas/metrics_yaml

metrics.yaml support
* add support for Tags in a charm
* removed whitelist checking
* common parsing function for categories and tags
* parse categories and tags directly