Add system variable to show whether libgroonga supports zlib/lz4 or not
Merge pull request #33 from naoa/check-libgroonga-support-zlib/lz4

Add system variable to show whether libgroonga supports zlib/lz4 or not

Patch by Naoya Murakami. Thanks!!!
test: use mroonga_libgroonga_support_lz4 and _zlib after loading Mroonga

Because we can't use them before loading Mroonga.
Drop MySQL 5.1 support

`my_free()` accepts only one argument in MySQL 5.5 or later.
cmake: drop MySQL 5.1 support

Explicitly error generates if one uses MySQL < 5.5.0.
Drop MySQL 5.1 support

Use `mysql_mutex_t` instead of `pthread_mutex_t`.
Fix variable declaration block
Unindent
mysql57: add new include directory

Mroonga can't be built with MySQL 5.7 yet. MySQL 5.7 has many API
changes... :<
mysql57 configure: add new include directory
doc: add mroonga_libgroonga_support_zlib/lz4 variables
doc: add How to specify the normalizer section
doc: add How to specify the token filters section
doc: add How to specify Groonga's column flags section
doc :fix missing "
doc: fix needless translation
Merge pull request #34 from naoa/doc-add-mrn_libgroonga_support_zlib/lz4-variables

doc: add mroonga_libgroonga_support_zlib/lz4 variables

Patch by Naoya Murakami. Thanks!!!
Merge pull request #35 from naoa/doc-fix-tutorial

doc fix tutorial

Patch by Naoya Murakami. Thanks!!!