Merge version number bump and NEWS file from master

NEWS

 Noteworthy changes in release a.b
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
+Noteworthy changes in release 1.8 (3rd April 2018)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
 * The URL to get sequences from the EBI reference server has been changed
   to https://.  This is because the EBI no longer serve sequences via
   plain HTTP - requests to the http:// endpoint just get redirected.

bgzip.1

-.TH bgzip 1 "26 March 2018" "htslib-1.7" "Bioinformatics tools"
+.TH bgzip 1 "3 April 2018" "htslib-1.8" "Bioinformatics tools"
 .SH NAME
 .PP
 bgzip \- Block compression/decompression utility

htsfile.1

-.TH htsfile 1 "26 January 2018" "htslib-1.7" "Bioinformatics tools"
+.TH htsfile 1 "3 April 2018" "htslib-1.8" "Bioinformatics tools"
 .SH NAME
 htsfile \- identify high-throughput sequencing data files
 .\"

tabix.1

-.TH tabix 1 "26 January 2018" "htslib-1.7" "Bioinformatics tools"
+.TH tabix 1 "3 April 2018" "htslib-1.8" "Bioinformatics tools"
 .SH NAME
 .PP
 tabix \- Generic indexer for TAB-delimited genome position files

version.sh

 #!/bin/sh
 
 # Master version, for use in tarballs or non-git source copies
-VERSION=1.7
+VERSION=1.8
 
 # If we have a git clone, then check against the current tag
 if [ -e .git ]