ENH create_dirs argument to SourceCache and BuildStore
start work on YAML-based frontend
remove transform_rules dead end
example yml files
frontend: rules in lists
WIP on file inclusion
frontend: wip on flattening parser
frontend: selecting most specific option
frontend: first working version of parser
serialize to build.yml as well for better readability
WIP first pass in refactoring Recipe to take **attrs
stack spec parser: recursively merging dict structure
REF move substitute to hashdist.core.utils
hdist use: basic querying of attrs working; next step: schema
marked_yaml: loading YAML with source loc annotation
REF marked_yaml.marked_{,yaml_}load
BUG parse_stack_spec: Preserve dict structure/have empty dicts
parse_stack_spec: include_keys arg to evaluate_dict_with_conditions
WIP pipeline system for processing yaml stack spec into build artifacts
split configuration and assemble(-build-spec) pipelines