also update DESCR to add some information from upstream about why it's fast,
ok with Florian.
* Searching for literals (no regex) uses Boyer-Moore-Horspool strstr.
* Files are mmap()ed instead of read into a buffer.
* Regex searches use PCRE 8.21+'s JIT compiler.
* Ag calls pcre_study() before executing the regex on a jillion files.
* Instead of calling fnmatch() on every pattern in your ignore files,
non-regex patterns are loaded into an array and binary searched.
* Ag uses Pthreads to take advantage of multiple CPU cores and search
files in parallel.
36c316f56f