create a ToDo file to document work needed on Altus Metrum products

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+- rationalize LED current limiting resistors to use 1k everywhere except
+  TeleLaunch products using high-intensity, sunlight-readable LEDs that need
+  different values
+
+- switch all 32 MHz and 40 MHz crystals to a 2.0x1.6 mm packages, using a 
+  footprint that has the outside dimentions of the ECX-1637B and inter-pad 
+  spacings from the Murata XRCGB40M000F1S1LR0 to ensure we can change crystals 
+  over time if needed.
+
+  - switch all STM32 based products to 32 MHz crystals for the SOC except
+    TeleDongle, which could move to an STM32F042 and sync to USB with no 
+    crystal.  Absolute crystal specs aren't very important here, but it's 
+    hard not to spend a fracton of a cent more for parts Bdale likes...
+
+       best choice:            DK 490-14308-2-ND
+
+  - switch all CC1200 based products to 40 MHz crystal in 2.0x1.6 mm package,
+    with the possible exception of TeleMini/TeleMicro if that's just too hard.
+    We care about frequency accuracy and stability for these.
+
+       cheapest credible:      DK XC3069TR-ND
+       currently available:    DK 490-XRCGB40M000F1S1LR0TR-ND
+