Added count argument to disk read/write

The count argument in disk_read() and disk_write() is now passed to the
FATFileSystem instance. This allows more efficient disk drivers to be
written that can read and write multiple sectors at a time.
Using jinja2 environment to load the template file.

This enables the use of template inheritance, see
http://jinja.pocoo.org/docs/templates/#template-inheritance
For this commit, renamed GHI_MBUINO to OC_MBUINO as required for the platform change as well as the TARGET_GHI_MBUINO to TARGET_OC_MBUINO directory.
add missed port
Merge pull request #448 from xiongyihui/stm32f407

add missed port for DISCO_F407VG
Merge pull request #445 from Experiment-626/master

Renamed TARGET_GHI_MBUINO to TARGET_OC_MBUINO to match the new name of t...
Merge pull request #443 from neilt6/master

Added count argument to disk read/write
Merge pull request #444 from chrta/enable_jinja_template_inheritance

Enable the use of template inheritance for exporters