Document how to build from git, and how to get jars from maven repo.

Document that we require maven 3.2, because of
https://jira.codehaus.org/browse/MNG-3385, fixed in maven 3.1.0-alpha-1.
That bug is minor, and maven 3.0 works fine for most purposes.

Add video links.
Add test case for [OPTIQ-411] duplicate column aliases
[OPTIQ-412] RelFieldTrimmer: when trimming SortRel, the collation and trait set don't match
Bad package name in package-info was causing errors in Eclipse.
[OPTIQ-414] Bad class name in sqlline shell script
[OPTIQ-413] Add RelDataTypeSystem plugin, allowing different max precision of a DECIMAL
Fix javadoc error.
[OPTIQ-416] Execute logical RelNodes using an interpreter
[OPTIQ-376] Move SqlRun into its own artifact

Now: {groupId: "net.hydromatic", artifactId: "quidem"}
[OPTIQ-421] Add COVAR_POP and COVAR_SAMP aggregate functions

Close apache/incubator-optiq#14

Pull requests closed by other recent changes (committed already):
Close apache/incubator-optiq#12
Close apache/incubator-optiq#5
Close apache/incubator-optiq#2
[OPTIQ-425] Add FilterAggregateTransposeRule, that pushes a filter through an aggregate.
[OPTIQ-426] Pool JDBC data sources, to make it easier to pool connections

Also pool OptiqConnection objects in OptiqSqlOperatorTest.
[OPTIQ-427] Off-by-one issues in RemoveDistinctAggregateRule, AggregateFilterTransposeRule
[OPTIQ-427] Off-by-one issues in RemoveDistinctAggregateRule, AggregateFilterTransposeRule
[OPTIQ-430] Rename project from "Optiq" to "Calcite"
Add recent presentation to README.md.
Covariance function - allow 2 arguments
[OPTIQ-422] Add REGR_SXX and REGR_SYY regression functions
Add tests inspired by Derby bugs.
Update history.