Some development boards do not have sufficient external pull-ups on
SD card pins. Most notably, if high level on GPIO13 is not registered
by the card when GO_IDLE_STATE command is received, the card will enter
SPI mode and further communication will not be possible, until power to
the card is toggled.
This change enables internal pull-ups on SD card pins in an attempt to
make this initialization process more reliable.
* Use "example" in all example function & variable names,
ie use i2c_example_xxx instead of i2c_xxx for example functions.
Closes#198https://github.com/espressif/esp-idf/issues/198
* Mark example functions, etc. static
* Replace uses of "test" & "demo" with "example"
* Split the UART example into two
* Rename "main" example files to end with "_main.c" for disambiguation
