*Code generate support for IDataLoader
*Make TextLoader API code generated so that it's at functional parity with the text loader in the ML.Net infrastructure.
*Move TextLoader API under Microsoft.ML.Data namespace
*Add convenience TextLoader API.
*Add error checking for invalid loader arguments such as ordinal, column names.
*Update baselines.
*Update samples with new loader API and backward compatibility with old loader API.

Migration of some existing internal documentation, rephrased in some places to be more appropriate in context (hopefully successfully). Related to #160, though this PR would be just part of addressing the issue of moving over internal docs.

* added ceiling to mathutils and have parquetloader default to sequential reading instead of throwing

* factor out sequence creation and add check for overflow in MathUtils

…ph variable outputs (#152)

* Adding support for training metrics in PipelineSweeperMacro and needed support files. Also includes new output information in PipelineSweeperMacro output graph to make consumption of returned pipelines easier.

* Changed where XML comment was placed.

* Added more tests (uncommented and fixed) for auto inference. Changed magic number in AutoMlUtils to be mix double value, per review comment.

* Added another test, TestPipelineSweeperMacroNoTransforms.

* Updated tests to include warning disabling (following Zeeshan S's example) to get build working.

* Changes to checks in AutoMlUtils (more correct usage of them).

* Fixing issue with ExceptParam using value and not name of parameters.

* Fixing errors on use of ExceptParam.

* Reduce number of hash bits in stratification column and add a unit test.

* Address PR comments.