build: updating history with major changes since v1.3.1
## Latest improvements ##
+ * autotest
+ - runs with random seeds (based on time) for diveristy
+ - output .json file for post-analysis
+ * build
+ - cleaned up compiler warnings across most platforms
+ - incorporated continuous integration script
+ - compact header APIs across all interfaces in liquid.h
+ - consistent build across Linux and macOS
+ * agc
+ - added more convenience methods, improved autotest stability
+ * fft
+ - spwaterfall less verbose with more convenience methods
+ * filter
+ - new rresamp family of objects to implement rational rate
+ resampling; very useful for fixed buffer sizes
+ - resamp now uses fixed-point phase for faster computation
+ - fixed issues with msresamp2 ordering to have expected roll-off
+ performance
+ - added notch filter design option for firfilt (with autotest)
+ * framing
+ - completely reworked msource family of objects to use firpfbch2
+ family of objects for computationally efficient
+ - added preliminary fskframe generator and synchronizer objects
+ * math
+ - improved functions for speed, is_prime()
+ - improved stability and consistency of root-finding algorithms
+ * multichannel
+ - added new firpfbchr family of objects for arbitrarily setting
+ number of channels and down-sampling rates
+ * modem
+ - refactored objects for amplitude modulation/demodulation to use
+ Hilbert transform, added autotest scripts
+ * nco
+ - improving consistency across platforms
+
## Improvements for v1.3.1 ##
* improved selection of SSE/MMX extension flags for gcc
