Add open_raster function for multiple band data.

Note that this has not been rigorously tested and probably won't
work even in the simplest of cases.
Add some rudimentary error handling to open_raster and write_raster

An error in opening the dataset (say a mistyped input string) will
now kill the opening process before it tries to open the raster and
get metadata. Likewise, an error in write_raster will kill the
process and neatly report to you where it had trouble.
Revert "Add open_raster function for multiple band data."

This reverts commit 6c86fb4493dfe91acb769d34c44963af9c77d60e.
Merge branch 'error_handle'

If an error was thrown during the open_raster procedure, the procedure
kept going with a null pointer to the dataset. This commit basically
handles the errors and kills the procedure if necessary.
Fix some silly typos
Pass default parameters to open_raster

If one calls open_raster(input), it will pass the default band 1
and access GA_ReadOnly (0) to open_raster
Fix another typo
Add check_create function to check whether a raster can be written using a given driver
Add functions to list the available drivers and test for the presence of a driver
Fix a silly mistake in raster_type_convert
Merge branch 'create_methods'

Conflicts:
	src/GDAL.jl

create_methods branch adds a check_create function
check_create(driver,method) lets you test whether a driver
supports the Create() method (default method=0) or the
CreateCopy() method (default method=1)
Make the check_create more logical; update README

check_create now returns false if the driver doesn't support
the given method rather than throwing an error.
Fix a typo in README.md
Add the new visualization process in GIS.jl to the GDAL.jl README