Add CHANGES file.
Add a block that extracts the central frequency of the received signal.

https://trello.com/c/uHzpnaeK

There are still some problems with attenuation jumps. So for debugging
purposes a new block that will track the central frequency is necessary.
Merge branch 'master' of repo.ijs.si:satprosi/gr-beacon
Update installation details in README

There were a few incompletenesses that are now corrected. No changes
in code were made.
Correct identation
Add scaling factor before conversion from linear to log. Fix input extraction in central_frequency.py

Without scaling, values of power were about 30dBx at no presence of signal and about 75dBx at full signal.
At these levels sensitivity of log function is too small to adequately represent scintillation. With
scaling, signal is normalized before conversion to log. Power output levels are now in the range from
-50dBx to 0dBx.

In central_frequency block, input vector extraction is changed. See code for details.
Merge branch 'master', remote-tracking branch 'origin/master'
Add new block that writes a scalar value to file along with timestamp.

Before there was no block that would write a scalar value to text file. Block
write_to_txt_f.py changes the value by multiplying it with -100 and trimming
it to 4 characters. New block operates exactly the same as write_to_txt_f.py
without altering the input value.
Change bandwidth for spectrum estimation.

Why is this change necessary?
Beacon is expected on the DC component, thus only 1/5 of total bandwidth around
DC component is considered for peak search and power estimation. Otherwise block
behaves as before.
Modify power format in write_to_file_block

Before multiplying and trimming power to 5 characters sometimes
was not adequate to represent the calculated power and small variations
were filtered out. Now the multiplication was removed and number of
characters was increased to 6.
Write another block that outputs peak value of signal.

This change is necessary for testing purposes. beacon_peak_ff block ou-
tputs only the peak magnitude of the signal in spectrum.
Added files that should be in previous commit.