Fix issues in tcell renderer and Windows build

- Fix display of CJK wide characters
- Fix horizontal offset of header lines
- Add support for keys with ALT modifier, shift-tab, page-up and down
- Fix util.ExecCommand to properly parse command-line arguments
- Fix redraw on resize
- Implement Pause/Resume for execute action
- Remove runtime check of GOOS
- Change exit status to 2 when tcell failed to start
- TBD: Travis CI build for tcell renderer
    - Pending. tcell cannot reliably ingest keys from tmux send-keys

src/reader.go

@@ -4,7 +4,6 @@ import (
 	"bufio"
 	"io"
 	"os"
-	"runtime"
 
 	"github.com/junegunn/fzf/src/util"
 )
@@ -44,7 +43,7 @@ func (r *Reader) feed(src io.Reader) {
 		if len(bytea) > 0 {
 			if err == nil {
 				// get rid of carriage return if under Windows:
-				if runtime.GOOS == "windows" && byteaLen >= 2 && bytea[byteaLen-2] == byte('\r') {
+				if util.IsWindows() && byteaLen >= 2 && bytea[byteaLen-2] == byte('\r') {
 					bytea = bytea[:byteaLen-2]
 				} else {
 					bytea = bytea[:byteaLen-1]