feat: revise API, add README.md, LICENSE (#2)

Co-authored-by: Dmitry Fedotov <dmitry@uint32.ru>
Co-committed-by: Dmitry Fedotov <dmitry@uint32.ru>

README.md

@@ -0,0 +1,137 @@
+# package script
+
+This package is intended as a collection of helper functions and tools fow quick construction of scripts that process .csv tables.
+
+Note that this is a work in progress. API is not guaranteed to be stable.
+
+## Example usage
+
+This demonstrates a very basic case: reading from stdin, checking whether array len is 2 and switching array elements.
+
+```go
+package main
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"os/signal"
+	"syscall"
+
+	"code.uint32.ru/dmitry/script"
+)
+
+func main() {
+	ctx, stop := signal.NotifyContext(context.Background(), syscall.SIGTERM, syscall.SIGINT)
+	defer stop()
+
+	reader := script.NewStdinReader()
+	writer := script.NewStdoutWriter()
+
+	processor := func(_ context.Context, in []string) ([]string, error) {
+		if len(in) != 2 {
+			return nil, errors.New("incorrect input len")
+		}
+
+		return []string{in[1], in[0]}, nil
+	}
+
+	conf := script.RunConfig{
+		Input:     reader,
+		Output:    writer,
+		Processor: processor,
+	}
+
+	if err := script.Run(ctx, conf); err != nil {
+		fmt.Println(err)
+	}
+}
+```
+
+A more conplicated example featuring a processor which is itself a struct with external dependency.
+
+```go
+package main
+
+import (
+	"context"
+	"fmt"
+	"os/signal"
+	"syscall"
+
+	"code.uint32.ru/dmitry/script"
+)
+
+// ExternalDep represent an external dependency
+// which your script utilizes. This can be a DB connection etc.
+type ExternalDep interface {
+	QueryID(string) ([]string, error)
+}
+
+type Processor struct {
+	dep ExternalDep
+}
+
+func New(e ExternalDep) *Processor {
+
+	return &Processor{
+		dep: e,
+	}
+}
+
+func (p *Processor) Process(ctx context.Context, in []string) ([]string, error) {
+	var out []string
+
+	result, err := p.dep.QueryID(in[0])
+	if err != nil {
+		// you can as well record the error and continue
+		// processing without yielding the error here
+		return nil, err
+	}
+
+	out = append(out, result...)
+	out = append(out, "processed")
+
+	return out, nil
+}
+
+func main() {
+	ctx, stop := signal.NotifyContext(context.Background(), syscall.SIGTERM, syscall.SIGINT)
+	defer stop()
+
+	r, err := script.NewCSVReader("/tmp/some_file.csv")
+	if err != nil {
+		panic(err)
+	}
+
+	defer func() {
+		if err := r.Close(); err != nil {
+			fmt.Println("err closing reader", err)
+		}
+	}()
+
+	w, err := script.NewCSVWriter("/tmp/some_output.csv")
+	if err != nil {
+		panic(err)
+	}
+
+	defer func() {
+		if err := w.Close(); err != nil {
+			fmt.Println("err closing writer", err)
+		}
+	}()
+
+    // intializing the processor
+	p := New(ExternalDep(nil))
+
+	conf := script.RunConfig{
+		Input:     r,
+		Output:    w,
+		Processor: p.Process, // Process implements script.Processor
+	}
+
+	if err := script.Run(ctx, conf); err != nil {
+		fmt.Println(err)
+	}
+}
+```