Use "$(MAKE) -C ..." for running make in subdirectories.

This adds announcements on changes of directory, helping see what happens
better.
Link correctly against a non-installed libcurl.
Have the makefile include local.mk if it exists.

This is to allow setting local variables in a persistent way.
Constify a few methods.
Small reformatting in sqlite_db.cc.
Add requirements.txt to python script
Merge pull request #36 from kovrus/python-script-installation

Add requirements.txt to python script, facilitating easy installation of python pre-requirements using pip.
Add Ruslan Kovalov to the AUTHORS/CONTRIBUTORS files.
Use built-in linking rules (with its own variables).
Refer to the json-c library as per their examples.

Not using -I makes more sense to me, but it appears that some distributions
put the headers in different locations, and all the example code refers only
to json.h, so we'll follow suit...

Also link against the correct library.
Remove some unneeded whitespace.
Add a .md extension to go/README.
Update the content of go/README.md to Markdown.
Convert go/README to Markdown format.
Remove the nearly useless go/ENV file.
Reformat merkle_tree_go.cc.
Fix a crash in the monitor.

This patch set fixes a crash in the monitor loop in case of receiving an STH
with just an increased timestamp (i.e. tree size does not change).

It also logs non-critical network problems while fetching STHs.