DV8

Mainly this release adds

• support for Definitions Version 8
• warnings for overlapping files (it's a start - more work still needed)
• some documentation about the current state of releasing for ybd itself
• foo.no-build as cache_key for 'no-build' mode, to avoid accidental empty artifacts

32616da Various readme fixes
3393fe7 Revert "Add a gash .travis.yml file"
20108d6 First pass notes on releasing
cfc8289 Add a gash .travis.yml file
5c8f125 fs is now a dependency
4072533 Add support for Definitions VERSION 8
2d7f4c9 Tidyup riemann code to lose some lines
1f66db5 Fix copyright year
da771a5 Split out write_metafile function
ffaf1af No need for chdir
2bbe3d8 Rename regexps => rules, and move logic to compile_rules
e30cf75 Split out compile_regexps function
9f020cd Clusters add to task count too
345498c Pep8
cbbff09 get_metadata requires definition, not path
141d3c5 metafile was not declared
0a009b0 Set no-build cache_keys to '.no-build'
e55ba30 No need for 'safename', definition['name'] is now safe
76bb5ae Fix misplaced bracket from 6f0533f
4659eb3 WIP - report where the overlaps are
cafab9e Only report overlaps once
6f0533f Use setdefault
7055554 Update readme with pyfilesystem dependency
4797a47 Merge pull request #179 from locallycompact/lc/osfs-broke
38b8df4 Revert "Use setdefault"
81dc395 Revert "Use OSFS in set_mtime_recursively"
1b85701 Missed bracket
f67fcb1 Merge pull request #178 from locallycompact/lc/osfs
4a4bb06 Dictionary notation
7f5e038 Replace mark_used_path with lambda expression
3da20cc Use OSFS to walkdirs
ba8cdd0 Use OrderedDict comprehension
8f1fd90 Use OrderedDict for regexps
1506a05 Chunk products is an array, not a dict
4503ce4 Use MultiFS in find_extensions
8066267 Use OSFS in detect_format
974a6b9 Use OSFS in set_mtime_recursively
3fd7e8e Use setdefault
3d93738 Code reduction in load_schemas
3af68b7 Report which meta files contain overlaps
c2f7c0e Report overlapping files when creating systems