highlight the existence of git 'tree' object type to distinguish it (e.g. from file system tree)
Extend/improve "Diffing Binary Files" section v2

v2:
  * grammar fixes
  * description of img2txt is dropped
[pl] translation of section 9.4
[pl] translation of section 9.5
Merge pull request #466 from gibas/09-git-internals

[pl] translation of sections 9.4 and 9.5
[pl] translation of section 9.6
Merge pull request #467 from gibas/09-git-internals

[pl] translation of section 9.6
[pl] translated section 9.7
Correct Typo
Correct typo 'commited' to 'committed'. Burnishing is going on!
Merge pull request #469 from gibas/09-git-internals

[pl] translated section 9.7
[pl] spelling fixes
[pl] s/email/e-mail/g
Merge pull request #471 from Rabierre/master

Correct Typo
Merge pull request #470 from gibas/spelling-fixes

[pl] Spelling fixes
[fi] Fixed grammar and typos
[fi] Apply all updates.
[fi] Fixed grammar near the inline code blocks.
[fi] Completed Chapter 2.2
[pl] first part of translation of chapter 7
Merge pull request #473 from gibas/07-customizing-git

[pl] first part of translation of chapter 7