Fix a bug that select --query _key:XXX for Int*/UInt* doesn't work

It is caused only TABLE_PAT_KEY because GRN_OP_GET_VALUE in
grn_expr_exec() uses grn_obj_get_value_() (see the last "_") instead
of grn_obj_get_value(). get_value_() is lighter version of
get_value(). get_value_() doesn't support key decoding. TABLE_PAT_KEY
encodes int/uint/geo point/float key. So we can't use get_value_() for
Int*/UInt*/*GeoPoint/Float.

This change uses get_value() to get column value. (_key is a pseudo
column.)
Use grn_obj_get_value_() if available

We cannot use grn_obj_get_vaue() only for patricia trie key
accessor. So we don't use grn_obj_get_value_() only for patricia trie
key accessor case.
doc en: fix too short under line
doc ja: translate po
Support two or more indexes for a table key

If there are two or more indexes for a table key, loading a new key to
the talbe may crash.
Support X + Y, X >> Y and X >>> Y operations for Int8 type

Other operations such as X - Y will be also supported by this
change. But they are not tested yet.

I wanted to support one operation per a commit but this change is the
minimum change. :<
Add a test for X - Y for Int8 type
Add a test for X * Y for Int8 type
Add a test for binary operation for Int8 type

Operation: X / Y
Add a test for binary operation for Int8 type

Operation: X % Y
Add a test for binary operation for Int8 type

Operation: X << Y
Add a test for binary operation for Int8 type

Operation: X | Y
Add a test for binary operation for Int8 type

Operation: X ^ Y
Add a test for binary operation for Int8 type

Operation: X & Y

TODO: Add tests for assign family such as +=.
Merge pull request #54 from groonga/support-two-or-more-indexes-for-a-key

Support two or more indexes for a table key
3.0.1 -> 3.0.2

make update-version NEW_VERSION=3.0.2
doc: remove needless section

I'll plan the sections of "load" command to follow one of "select":

load
  Summary
  Syntax
    (including description of arugments)
  Usage
  Return value
doc: translate each section in "load"

refs #1661

In previous commit message, I said "including arguments (it is wrong,
"parameters" correctly) in Syntax", but I separate them because of few
many parameters.
doc: re-arrange the order of sections in "load" command document

Before:          After:
  Syntax           Summary
  Summary          Syntax
  Parameters       Parameters
  Return value     Usage
  Usage            Return value
  See also         See also
doc: translate "load" document from ja to en