Submodule GitExtensionsDoc updated

Submodule GitExtensionsDoc:
    > c357813 - Google code deprecated downloads. SourceForge becomes the official download page.
    > 51f6ff4 - Fix readme and Chapter 1
    > 8025fa8 - Fix HTML Help command name (cherry picked from commit ed27d9b10be125fdd80bd5106d073569325974eb)
    > 9f86973 - Ignore *.orig
    > 0ae324b - Changed URL location to officiall site.
    > 9cb90d0 - Typo (cherry picked from commit 0586c61e8ec0bb78c1645010dec7932c57264368)
    > 00e3900 - Readme fix (cherry picked from commit 85054c75c5bb995211bb181d0a01f5529cce5141)
    > dea5f5e - Update readme (cherry picked from commit 2e6c3f072caa3d0c4c2dc83acd1ef1a0e3989730)
    > 0cfb2c9 - Chapter 1 fixes
    > 6c4749c - Fix Issue #8 - Empty pages in generated PDF (cherry picked from commit cdedd28ad60ab9de923290e8738bd2883951209b)
    > 06c9784 - Change table formatting and filename so PNG is displayed
    > c96b277 - Remove indexing statements
    > 8ba30c6 - Correct formatting in Mac Installation section
    > eec62cc - Correct name of Python config file (cherry picked from commit 1645bb4e4841d04d66f2b8ee77fe5467f3656e57)
    > ed27d9b - Fix HTML Help command name
    > bfc2fa4 - Changed URL location to officiall site.
    > 0586c61 - Typo
    > 85054c7 - Readme fix
    > abf41f6 - Make warning clearer
    > 2e6c3f0 - Update readme
    > d91da04 - Chapter 1 fixes
    > cdedd28 - Fix Issue #8 - Empty pages in generated PDF
    > 808e96a - Change table formatting and filename so PNG is displayed
    > 62fd53e - Remove indexing statements
    > e062ed8 - Correct formatting in Mac Installation section
    > 1645bb4 - Correct name of Python config file