Improve documentation around ancestry field and collation

[kbrock]

dependency:

• Document and test with column collation #601 (this updates those comments)
• Add default ancestry format and primary key format #612

postgres: binary data type is not currently working
mysql: binary data type or string with binary collation is working

Had wanted to go with a binary for all database, but the test would not pass.
So I backtracked a little, researched opclasses, preferring ascii where possible.

This updates the comments introduced in #601

[kbrock]

@kshnurov I updated the gem to use binary for postgres. The test suite puked.

Staying with the original comments, but put in more documentation to hopefully get this running correctly.

[kshnurov]

@kshnurov I updated the gem to use binary for postgres. The test suite puked.

Ok, after some digging it turns out postgres returns bytea in hex format and pg gem doesn't unescape it by default.
Here's a quick solution for postgres, it should also solve this

ALTER DATABASE dbname SET bytea_output to 'escape';

With this one, tests are green unless we use update_strategy = :sql.
regexp_replace isn't possible with binary columns. I'd suggest removing :sql update strategy completely.

Another solution is to call connection.unescape_bytea on ancestry field, but I don't wanna dig into it since I'm using mysql right now.

[kbrock]

@kshnurov For a binary ancestry column, what else do I need to specify to set a length? And what value should I use?

 Mysql2::Error: BLOB/TEXT column 'ancestry' used in key specification without a key length (ActiveRecord::StatementInvalid)

[kshnurov]

For a binary ancestry column, what else do I need to specify to set a length? And what value should I use?

IDK if you missed this comment
It definitely shouldn't be a BLOB.

[kbrock]

update:

• provided simplified column information and a section with probably way too much detail. After time, this can probably be simplified.
• Added details about using/preferring materialized_path2
• Added configuration file step to default to materialized_path2