Errors and lacks in document "Pig Latin Basics"

This is a patch to fix errors and lacks in document "Pig Latin Basics".

1. States that COGROUP groups records with a null key from different relations separately.
2. "A map key must be a scalar chararray "
3. Removes a statement which says that a star expression is a tuple expression (it seems incorrect)
4. Fixes a subject confusion of a sentence "When two bytearrays are used in arithmetic expressions..."
5. Updates a link to Java API documentation.
6. Fixes a tuple example: "LOAD 'data' as..." -> "A = LOAD 'data' as..."
7. "the asterisk (*) is used to project all tuples fields "
8. A result of COGROUP with two relations contains three fields, not two
9. Removes an example of COGROUP INNER, which is deprecated
10. Removes a sentence which says "JOIN operator always performs an inner join". Actually, JOIN also perform an outer join.
11. JOIN "Performs an outer join of two ore more relations"
12. Replaces an example of "-Dpig.additional.jars" with a jar file on HDFS. The current version incorrectly shows an example of a Pig script on HDFS.
13. Fixes typos, lack of hyperlinks, inappropriate indentation, and incorrect chaptering.