Now src contains exactly what's embedded in mongoose.c and .h, nothing more.
Added `tools/amalgam.sh` to aamlgamate both files at once.
There are no functional changes to mongoose.c, .h in this PR, only slight filename changes.
Now it also tries to find the included file relatively to the "parent"
file. This is required for amalgamation of the frozen into mjs, since
`frozen.c` includes `frozen.h` instead of `frozen/frozen.h`.
PUBLISHED_FROM=8f670a1509a30cfdfb22e454b7851f4cf28fb98d