Added License block to README.md
Revert issue #99 fixes

There are two commits involving issue #99 which should be reverted.

First of all, #99 is not an issue in Arel at all. Second, the fix provides pretty much destroys the purpose of pagination by cause full table scans.

The original code (it seems I can't simply revert the commits) is 900 times slower than this one.

```
SELECT * FROM (
   SELECT raw_sql_.*, rownum raw_rnum_
   FROM (SELECT "LANCAMENTOS".* FROM "LANCAMENTOS" ) raw_sql_
 )
 WHERE raw_rnum_ between 1 and 30

----------------------------------------------------------------------------------
| Id  | Operation           | Name        | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------
|   0 | SELECT STATEMENT    |             |  4636K|  2701M| 23442   (2)| 00:04:42 |
|*  1 |  VIEW               |             |  4636K|  2701M| 23442   (2)| 00:04:42 |
|   2 |   COUNT             |             |       |       |            |          |
|   3 |    TABLE ACCESS FULL| LANCAMENTOS |  4636K|   738M| 23442   (2)| 00:04:42 |
-----------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   1 - filter("RAW_RNUM_"<=30 AND "RAW_RNUM_">=1)

   Statistics
-----------------------------------------------------------
               4  user calls
              13  physical read total multi block requests
       202588160  physical read total bytes
       202588160  cell physical IO interconnect bytes
               0  commit cleanout failures: block lost
               0  IMU commits
               0  IMU Flushes
               0  IMU contention
               0  IMU bind flushes
               0  IMU mbu flush

SELECT * FROM (
   SELECT raw_sql_.*, rownum raw_rnum_
   FROM (SELECT "LANCAMENTOS".* FROM "LANCAMENTOS" ) raw_sql_
   WHERE rownum <= 30
 )
 WHERE raw_rnum_ >= 0

-----------------------------------------------------------------------------------
| Id  | Operation           | Name        | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------
|   0 | SELECT STATEMENT    |             |    30 | 18330 |     2   (0)| 00:00:01 |
|*  1 |  VIEW               |             |    30 | 18330 |     2   (0)| 00:00:01 |
|*  2 |   COUNT STOPKEY     |             |       |       |            |          |
|   3 |    TABLE ACCESS FULL| LANCAMENTOS |    30 |  5010 |     2   (0)| 00:00:01 |
-----------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   1 - filter("RAW_RNUM_">=0)
   2 - filter(ROWNUM<=30)

   Statistics
-----------------------------------------------------------
               4  user calls
               0  physical read total multi block requests
               0  physical read total bytes
               0  cell physical IO interconnect bytes
               0  commit cleanout failures: block lost
               0  IMU commits
               0  IMU Flushes
               0  IMU contention
               0  IMU bind flushes
               0  IMU mbu flush
```
Update test_oracle.rb
Merge pull request #174 from eduardordm/master

Revert fixes involving issue #99 (which makes Arel unusable in large datasets)
ActiveRecord -> Active Record

As per the Rails documentation guidelines.
ARel -> Arel

The project uses "Arel" most of the time, but there were a few "ARel"
here and there. I checked with @brynary back in 2010 to pick one for
the Rails documentation guidelines and "Arel" was chosen and documented.
This patch chooses "Arel" vs "ARel" based on that.
Merge pull request #171 from topdev/master

Added License block to README.md
Updage Gemfile to use https URL
Release 4.0.0
Make visitors threadsafe by removing @last_column

The last_column feature of the ToSql visitor and its descendants is what
enabled quoting based on the column last visited -- in other words, if
you have a standard condition like an equality with a string attribute
on the left side and an integer on the right side, then when ARel visits
the node, it'll first visit the left side attribute, setting the
column of the string attribute as the last column, and resulting in the
right side of the condition getting the appropriate quoting.

The downside is that this means that visitors can't be shared between
threads, because of the state mutation. It also makes for some really
weird behavior in the event that the visitor visits a node that happens
to contain an attribute you weren't expecting to be there, since it'll
potentially quote something based on that attribute. So, it prevents
reversing an equality condition. column = value will work, but not value
= column, since the last column wouldn't be the column you're hoping
for.

This is a first pass at fixing this by changing the signature of the
visit methods to accept the currently-relevant attribute, if any.
Fixed typos
Merge pull request #181 from prathamesh-sonpatki/typos

Fixed typos
call super from initialize
record who created the node when $DEBUG is true
"Relational Database Managements systems", not "Relational Database Managements System systems"
Prettied up the README with syntax highlighting.

[ci skip]
Merge pull request #193 from parndt/patch-1

Prettied up the README with syntax highlighting. [ci skip]
Remove deprecated `Arel::Table.table_cache` with no replacement
Remove deprecated `Arel::Table#columns` with no replacement
Add licences to gemspec

Closes #197