Several punctuation fixes, add pointer to DS1307RTC lib.

The current (old) description claimded that the DS1307RTC
library is part of the download bundle, which is not (no longer?)
the case. Instead pointing to following now:
https://github.com/PaulStoffregen/DS1307RTC

Change-Id: I28b0c71398e56d50de0c786e4dee97d28f408481

Readme.md

@@ -89,15 +89,15 @@ illustrating how the library can be used with various time sources:
   A companion Processing sketch will automatically provide these messages
   if it is running and connected to the Arduino serial port.
 
-- `TimeSerialDateStrings.pde` adds day and month name strings to the sketch above
+- `TimeSerialDateStrings.pde` adds day and month name strings to the sketch above.
   Short (3 characters) and long strings are available to print the days of
   the week and names of the months.
 
 - `TimeRTC` uses a DS1307 real-time clock to provide time synchronization.
-  A basic RTC library named DS1307RTC is included in the download.
-  To run this sketch the DS1307RTC library must be installed.
+  The basic [DS1307RTC library][1] must be downloaded and installed,
+  in order to run this sketch.
 
-- `TimeRTCSet` is similar to the above and adds the ability to set the Real Time Clock
+- `TimeRTCSet` is similar to the above and adds the ability to set the Real Time Clock.
 
 - `TimeRTCLog` demonstrates how to calculate the difference between times.
   It is a very simple logger application that monitors events on digital pins
@@ -106,11 +106,11 @@ illustrating how the library can be used with various time sources:
 
 - `TimeNTP` uses the Arduino Ethernet shield to access time using the internet NTP time service.
   The NTP protocol uses UDP and the UdpBytewise library is required, see:
-  http://bitbucket.org/bjoern/arduino_osc/src/14667490521f/libraries/Ethernet/
+  <http://bitbucket.org/bjoern/arduino_osc/src/14667490521f/libraries/Ethernet/>
 
-- `TimeGPS` gets time from a GPS
+- `TimeGPS` gets time from a GPS.
   This requires the TinyGPS library from Mikal Hart:
-  http://arduiniana.org/libraries/TinyGPS
+  <http://arduiniana.org/libraries/TinyGPS>
 
 ## Differences
 
@@ -126,7 +126,7 @@ Changes in the Time library API:
 - function added to automatically sync time with external source
 - `localTime` and `maketime` parameters changed, `localTime` renamed to `breakTime`
 
-## Technical notes:
+## Technical Notes
 
 Internal system time is based on the standard Unix `time_t`.
 The value is the number of seconds since Jan 1, 1970.
@@ -151,5 +151,7 @@ breakTime(time, &tm);  // break time_t into elements stored in tm struct
 makeTime(&tm);         // return time_t from elements stored in tm struct
 ```
 
-The DS1307RTC library included in the download provides an example of how a time provider
+This [DS1307RTC library][1] provides an example of how a time provider
 can use the low-level functions to interface with the Time library.
+
+[1]:<https://github.com/PaulStoffregen/DS1307RTC>