Improve docs, add reference to GPS.

Author: peterhinch

HD44780/README.md

@@ -0,0 +1,38 @@
+# Driver for character-based LCD displays
+
+This driver is for displays based on the Hitachi HD44780 driver: these are
+widely available, typically in 16 character x 2 rows format.
+
+# Files
+
+ * `alcd.py` Driver, includes connection details.
+ * `alcdtest.py` Test/demo script.
+
+Currently most of the documentation, including wiring details, is in the code.
+
+# Display Formatting
+
+The driver represents an LCD display as an array indexed by row. Assigning a
+string to a row causes that row to be updated. To write text to a specific
+column of the display it is recommended to use the Python string `format`
+method.
+
+For exampls this function formats a string such that it is left-padded with
+spaces to a given column and right-padded to the specified width (typically the
+width of the display). This ensures previous contents are overwritten.
+
+```python
+def print_at(st, col, width=16):
+    return '{:>{col}s}{:{t}s}'.format(st,'', col=col+len(st), t = width-(col+len(st)))
+```
+
+```
+>>> print_at('cat', 2)
+'  cat           '
+>>> len(_)
+16
+>>> 
+```
+
+Similar use of the `format` method can be used to achieve more complex
+tabulated data layouts.

README.md

@@ -13,6 +13,11 @@ This GitHub repository consists of the following parts:
  * [A driver for the HTU21D](./htu21d/README.md) temperature and humidity
  sensor. This is intended to be portable across platforms and is another
  example of an asynchronous device driver.
+ * [A driver for character LCD displays](./HD44780/README.md). A simple
+ asynchronous interface to displays based on the Hitachi HD44780 chip.
+ * [A driver for GPS modules](./gps/README.md) Runs a background task to read
+ and decode NMEA sentences, providing constantly updated position, course,
+ altitude and time/date information.
  * [A modified uasyncio](./FASTPOLL.md) This incorporates a simple priority
  mechanism. With suitable application design this improves the rate at which
  devices can be polled and improves the accuracy of time delays. Also provides