Add MCP73831 battery charger.

2018-schematic/library/desertbus.dcm

@@ -1,3 +1,7 @@
 EESchema-DOCLIB  Version 2.0
 #
+$CMP MCP73831
+F https://cdn.sparkfun.com/datasheets/Components/General%20IC/33244_SPCN.pdf
+$ENDCMP
+#
 #End Doc Library

2018-schematic/library/desertbus.lib

@@ -1,6 +1,23 @@
 EESchema-LIBRARY Version 2.3
 #encoding utf-8
 #
+# MCP73831
+#
+DEF MCP73831 U 0 40 Y Y 1 F N
+F0 "U" -350 50 60 H V L CNN
+F1 "MCP73831" -350 -50 60 H V L CNN
+F2 "TO_SOT_Packages_SMD:SOT-23-5_HandSoldering" 0 -450 60 H I C CNN
+F3 "https://cdn.sparkfun.com/datasheets/Components/General%20IC/33244_SPCN.pdf" 0 -550 60 H I C CNN
+DRAW
+S -500 350 500 -350 0 1 0 N
+X STAT 1 -700 -200 200 R 50 50 1 1 I
+X VSS 2 700 -200 200 L 50 50 1 1 I
+X VBAT 3 700 200 200 L 50 50 1 1 I
+X VDD 4 -700 200 200 R 50 50 1 1 I
+X PROG 5 700 0 200 L 50 50 1 1 I
+ENDDRAW
+ENDDEF
+#
 # NODEMCU
 #
 DEF NODEMCU U 0 40 Y Y 1 F N