Support basic HTTP get file request

[jgfoster]

This supports /echo?key="value" requests and /path requests. Large files take a long time to transfer. Following are some measurements of time with different buffer sizes:

Buffer size: 128
file "/20210827.csv" has a size of 5713467
write = 5713467; freeMemory = 4640
timeInRead = 27661; timeInWrite = 79832; timeInFlush = 43

Buffer size: 2048
file "/20210827.csv" has a size of 5858009
write = 5858009; freeMemory = 2720
timeInRead = 11681; timeInWrite = 74739; timeInFlush = 3

Buffer size: 1024
file "/20210827.csv" has a size of 5878029
write = 5878029; freeMemory = 3744
timeInRead = 15108; timeInWrite = 72649; timeInFlush = 3

The entire process is blocking so there is a risk of leaving the bubbler on for minutes. Thus, the reading files feature should be considered a basic alternative to taking the device apart to read files.

[prestoncarman]

LGTM