Add new callbacks and fix null issues

• Merge branch 'fix_one_directional_swipe_items' 6bc293a
• Merge pull request #92 from sandstreamdev/all-contributors/add-derUli 5660993
• Fix one directional swipe items animation a98affe
• docs: update .all-contributorsrc [skip ci] 630a53d
• docs: update README.md [skip ci] 4541c1f
• Merge branch 'closes_issue_77' 3a28164
• Fix code review issues 57d7eda
• Fix code review issues 21809ba
• Update docs and uncomment tests 029adac
• Add documentation for new callbacks 4569d2f
• Add callback tests and guess fixes for null pointers 5496b2f
• Add optional flags for callbacks 3ddeb66
• Add typescript typings and change progress callback name d8fd22d
• Merge pull request #83 from sandstreamdev/all-contributors/add-przemyslawzalewski 7f77cbc
• docs: update .all-contributorsrc [skip ci] 672b949
• docs: update README.md [skip ci] d60e1d6
• Merge pull request #81 from sandstreamdev/adjust_example_page_typography 72c8c0d
• Merge pull request #82 from sandstreamdev/update_dependencies_23_01_2020 6b9254c
• Remove semver ranges from dev dependencies to keep them consistent with others 3fa8c51
• Remove no longer needed explicit git add command of lint-staged hooks bd024a5
• Drop Node 8 support b96f862
• Update package locks 8507599
• Update dependencies 90245d4
• Use more semantic header tag and provide fallback trigger texts 96f2ea9
• Adjust header margins to make them not stick to the chrome 591454e
• Give up and let stylelint take over formatting as the rules seems to be not be affected by disable rules 3e86c2e
• Center footer text content despite flexbox centering aea62e6
• Disable confused stylelint and prettier conflict 332e0f1
• Set default increased line height 04882c6
• Unify font-family style application 049f91e
• Closes issue 77 4a4180a
• Merge pull request #76 from sandstreamdev/greenkeeper/default/@sandstreamdev/react-swipeable-list-0.3.2 22e191d
• chore(package): update lockfile examples/package-lock.json 3388581
• fix(package): update @sandstreamdev/react-swipeable-list to version 0.3.2 57619c3

v0.3.2...v0.4.0