Create gsm_integration_code_update

Not sure if I'm following protocol here properly, Alex. This is an updated version of the main INO file. Main changes are:

-removed program control of the modem Rx pin (pin 3), which was hanging program flow
-simplified the display functions, saving a lot of calculation (numbers are assigned to specific digits on the seven-segment only once, instead of each time they are flashed for POV)
-correctly implemented the bit shift logic to allow easy swapout of common anode and cathode 
-put in a note on how to identify if a seven-segment display is common cathode or common anode
separate raw readings from NTU conversion
function format fix
fix annoying linewrap
Merge pull request #9 from iamchriskelley/patch-1

Create gsm_integration_code_update
merge gsm_integration_code_update into turbidimeter.ino
Delete gsm_integration_code_update

changes absorbed into firmware sketch
add circuit schematic source files
add a bibtex file of relevant literature
update software readme
add assembly instructions and hardware files
clear out old files
fix documentation
fix (?) markdown rendering issue
update File Extensions guide and rename to Dependencies
add calibration function
merge Master into GSM-integration