Add LZ4 compression instead of LZO compression
Merge pull request #223 from naoa/add-lz4-compression

Add LZ4 compression instead of LZO compression

Patch by Naoya Murakami. Thanks!!!
Keep backward compatibility for LZO remove
Share common code
lz4: add max size check
lz4: use "lz4_" prefix instead of "l"
lz4: break a long line
lz4: introduce "packed_value" and "packed_value_len" variables for readability

Because "lz4_value" and "lz4_value_len" didn't represent LZ4 compressed
data.
lz4: use more readable name
lz4: fix function name in error message
fix lz4 support reporting in --version

* In #223, lzo compression support dropped and add lz4 compression support.
Merge pull request #224 from cosmo0920/fix-support-reporting-lz4

fix lz4 support reporting in --version

Patch by Hiroshi Hatake. Thanks!!!
mruby: follow weight number may be int32 change
Use "Iu" for size_t on Windows
Make buildable on no atomic 64bit operation environment such as PowerPC

It makes buildable but it's not recommended to use on the environment.
You will see many warning messages on build.
Add output type accessor

It's not needed for normal Groonga C API users. Language bindings
developers may want to use it.
Add document of grn_content_type

TODO:
  * Update file list
  * Check build error (I don't build it yet. Sorry.)
test: follow LZO -> LZ4 change
Add "uncompressed_" prefix for readability